Symposium Organizers
Zhongyang Cheng Auburn University
Vivek Bharti 3M Company
Zhuo Xu Xi’an Jiaotong University
Debra A. Wrobleski Los Alamos National Laboratory
HH1: Dielectric Elastomers
Session Chairs
Monday PM, November 29, 2010
Back Bay B (Sheraton)
9:30 AM - **HH1.1
Hydrostatically Coupled Dielectric Elastomer Actuators: New Opportunities for Haptics.
Federico Carpi 1 , Gabriele Frediani 1 , Danilo De Rossi 1
1 Interdpt. Res. Centre 'E. Piaggio', University of Pisa, Pisa Italy
Show AbstractDielectric elastomer actuators (DEAs) have been demonstrated to represent today a high-performance technology for electromechanical transducers based on electroactive polymers. As a means to improve versatility and safety of DEAs for several fields of application, so-called ‘hydrostatically coupled’ DEAs (HC-DEAs) have recently been described. HC-DEAs are based on an incompressible fluid that mechanically couples a DE-based active part to a passive part interfaced to the load, so as to enable hydrostatic transmission. This paper presents ongoing developments of HC-DEAs and their promising potential application in the field of haptics. In particular, the first part of the paper describes a static and dynamic characterization of a prototype actuator made of two pre-stretched membranes (20 mm wide, 1.8 mm high, and 61 µm thick) of 3M VHB acrylic elastomer, coupled via silicone grease. The actuator exhibited a maximum stress of 1.3 kPa at 4.4 kV, a relative displacement of -80% at 4.4 kV, a -3dB bandwidth of 3 Hz, and a resonance frequency of 160 Hz. The second part of the paper presents possible applications of the tested actuator configuration for haptic interfaces. Two specific examples are considered. The first deals with a wearable tactile display used to provide users with tactile feedback during electronic navigation in virtual environments. The display consists of HC-DEAs arranged in contact with finger tips. As a second example of usage, an up-scaled prototype version of an 8-dots refreshable cell for dynamic Braille displays is shown. Each Braille pin consists of a miniature HC-DEA, with a diameter lower than 2 mm. Both types of application clearly show the potential of the new technology and the prospective opportunities for haptics.
10:00 AM - HH1.2
Highly Compliant Pressure Sensor Using Conductive Fluid in an Elastomeric Sheet.
Rebecca Kramer 1 , Yong-Lae Park 1 , Carmel Majidi 1 , Phil Berard 1 , Robert Wood 1
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractEmerging technologies such as wearable computing and stretchable electronics require the development of highly compliant and stretchable sensors that register the location and intensity of pressure or strain over a large area. We present a rapid monolithic fabrication technique for the development of an elastomeric sheet embedded with a network of conductive micro-channels that senses the location and intensity of localized pressure. The micro-channels achieve conductivity through the implantation and encapsulation of a conductive liquid, such as non-toxic eutectic gallium indium (eGaIn, BASF). Pressing or straining the surface of the elastomeric sheet at any point deforms the cross-section of nearby channels and changes their electrical resistance. The relative change in the electrical resistance of all of the channels within the network yields the location and intensity of applied pressure or strain. Sensitivity and resolution of the elastomeric pressure sensor is controlled by the geometry and spacing of the conductive micro-channels as well as the thickness and elasticity of the elastomer matrix. Pressure sensors with channel dimensions ranging from 25 μm to 1000 μm have been fabricated by casting polydimethylsiloxane (PDMS; Sylgard 184, Dow Corning; 10:1 mass ratio of elastomer base to curing agent) in a photoresist (SU-8 2010) mold that is patterned by means of a laser-based direct-write photolithography technique. Micro-channels of the desired dimensions are introduced into silicon wafers via direct-write laser exposure using a diode-pumped solid-state (DPSS) 355nm laser micromachining system. The system was previously calibrated to provide good exposure for SU-8 spin-coated to 40 μm in thickness. Elastomer micro-channels have been demonstrated with dimensions as small as 25 μm by 40 μm. Micro-channels of this size, and of other various dimensions, have been filled with conductive eGaIn and shown to maintain sensing functionality. Enhanced sensitivity of the elastomeric pressure sensor can be achieved through continued reduction of the micro-channel dimensions and increased density of the channel network. Multi-layered elastomeric channel networks may provide greater sensing capabilities due to perpendicular but non-intersecting channel designs. Moreover, the elastomeric sheet may be easily integrated with wearable electronics or robotic systems for combined on-board circuitry and sensing functionality.
10:15 AM - HH1.3
Controlled Improvement of Nanocomposite Properties for Dielectric Elastomer Actuators.
Denis McCarthy 1 , Hristiyan Stoyanov 1 , Dmitry Rychkov 1 , Huelya Ragusch 1 , Sebastian Risse 1 , Guggi Kofod 1
1 Institute of Physics & Astronomy, University of Potsdam, Potsdam, Brandenburg, Germany
Show AbstractHigh permittivity nanocomposites are being studied for use in a variety of fields. Classical theories, such as Bruggeman and Lichteneker, predict small permittivity increases at low amounts of high permittivity filler where the processing and mechanical properties of the composites are practical. Much higher permittivity increases than these predictions have been observed with nanocomposites suggesting large improvements are possible. The large increases observed in nanocomposites are normally accompanied by increased A.C. conductivity and different mechanisms have been suggested to explain these increases. Although none of these have been conclusive, it is clear the interface between the fillers and the host matrix is the source and control of the interaction between the fillers and matrix is key to achieving new, high performance nanocomposites in all fields. Increased conductivity of the interface layers in nanocomposites contributes strongly to the increased permittivity of composites, but it also influences the electrical breakdown and mechanical properties. It has been shown that increases in permittivity can be achieved without compromising the desired polymer properties.Dielectric elastomer actuators (DEA) are simple electrostatic actuators similar in design to a soft capacitor. Due to their low cost, simple production and impressive performance - stresses up to 7 MPa and strains of over 200%, DEA allow the design of new devices, and can replace other actuators in current devices. These devices also require new high permittivity materials, while maintaining high electrical breakdown, low losses and elastomeric mechanical properties in order to reduce operating voltages and increase actuation performance.We report the results of an investigation into TiO2-elastomer composites for DEA. We show that modifying the TiO2 particle surface changes the interaction between the polymer and filler and this can be used to achieve high permittivity composites with low loss, low mechanical reinforcement and improved actuation. By studying a range of TiO2 particles with different surface functionalisation the effects of the different filler particles, their surfaces can be identified and the requirements for improved composites identified. As predicted by the classical theories, increased filler content leads to increased permittivity, but the greater effect is the increased interface. Unlike the predictions of these theories, even at low filler content the permittivity of the filler has a significant effect on the composite permittivity. By controlling the interface we can increase the permittivity without degrading the other material properties, thus improving the actuation performance. Percolation of the interface layers and the particles is observed and this leads to detrimental effects on the electrical and mechanical properties. A targeted method to achieve improved composites will be suggested from these results.
10:30 AM - HH1.4
Dielectric Elastomer Generators: How Much Energy Can be Converted?
Soo Jin Adrian Koh 1 2 , Christoph Keplinger 3 2 , Tiefeng Li 4 2 , Siegfried Bauer 3 , Zhigang Suo 2
1 Large-Scale Complex Systems, Institute of High Performance Computing, Singapore Singapore, 2 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 3 Soft-Matter Physics, Johannes Kepler University, Linz Austria, 4 Institute of Applied Mechanics, Zhejiang University, Hangzhou, Zhejiang, China
Show AbstractDielectric elastomers are being developed as generators to harvest energy from renewable sources, such as human movements and ocean waves. We model a dielectric elastomer generator as a system of two degrees of freedom, represented either on the stress-stretch plane, or the voltage-charge plane. A point on such a plane represents a state of the generator, a curve represents a path of operation, a contour represents a cycle of operation, and the area enclosed by the contour represents the energy of conversion per cycle. Each mechanism of failure is represented by a curve in the plane. The curves of all the known mechanisms of failure enclose a region of allowable states. The area enclosed by these curves gives the theoretical maximum amount of energy that can be converted. Using realistic material models, it is found that natural rubber outperforms VHB elastomer as a generator at operating strains of less than 15%. Furthermore, by varying key material parameters like the small-strain shear stiffness, dielectric strength or dielectric constant, energy of conversion of 1.0 J/g is possible. The method presented in this study could aid in the selection and evaluation of elastomer materials as generators.
11:15 AM - **HH1.5
Environmental Power From Dielectric Elastomers.
Iain Anderson 1 2 , Thomas McKay 1 , Benjamin O'Brien 1
1 Biomimetics Laboratory, Auckland Bioengineering Institute, Auckland, Auckland, New Zealand, 2 Engineering Science, University of Auckland, Auckland New Zealand
Show AbstractLightweight and flexible Dielectric Elastomer (DE) artificial muscles are an attractive technology for environmental energy harvesting. Energy generated per cycle is governed by the amount of strain the polymer element is exposed to and is relatively independent of frequency. Thus the polymer elements of the generator can be directly coupled to structures perturbed by aperiodic sources such as water waves and wind. DE generators are primed with charge once per cycle, but the priming charge can be lost due to leakage. Also, high voltages are desirable as DE generator efficiency improves as the voltage of the priming charge is increased. We have developed a self-priming system that can boost voltage with every cycle and replenish charge that is used for priming the membrane. The self-priming circuit can also be started using another on-board energy harvester such as a solar cell array. In this presentation we demonstrate the proof-of-concept self-primed DEG by harvesting energy directly from a tree branch swaying in the wind.MethodsA two-membrane DEG assembly was produced so that both membranes (prestretched 3M VHB 4905 acrylic tape), moved in tandem. The self-priming circuit converted the generated energy to a higher charge form, and thus the voltage in the DEG system increased with every pump of the generator. Photovoltaic cells (Sanyo AM-1437 amorphous solar cells) were used for the initial charge. The generator membranes were coupled to a New Zealand pohutukawa tree branch exposed to wind gusts of up to 20 knots.Results and discussionInitial charge (~30V), was boosted to above 1 kV and this intensified during sustained wind gusts. The instantaneous voltage represented the net result of energy gained from wind excitation minus energy lost from charge leakage. This experiment has provided a practical demonstration of wind energy harvesting using a portable autonomous polymer self-primed DE generator.
11:45 AM - HH1.6
Bistable Electroactive Polymers with Tunable Transition Temperatures.
Xiaofan Niu 1 , Paul Brochu 1 , Zhibin Yu 1 , Qibing Pei 1
1 Materials Science and Engineering, University of California Los Angeles, Los Angeles, California, United States
Show AbstractBistable Electroactive Polymer (BSEP) is a new category of smart materials that is rigid at ambient conditions and turn into a dielectric elastomer at above the polymer’s glass transition temperature. The BSEP combines excellent shape memory property with dielectrically induced actuation to as high as 300% strain. We report that the glass transition temperature can be tuned in a broad range. As such, a series of new BSEP polymers are now available to meet the temperature requirements of different applications. Choosing the right BSEP could lower the energy consumption and response time in each actuation cycle. The actuation strain, shape fixity, and shape recovery of the new BSEP have been extensively characterized. Application for refreshable Braille displays will also be discussed using a BSEP polymer with a glass transition temperature suitable for direct touch.
12:00 PM - HH1.7
Artificial Muscles with Sense.
Iain Anderson 1 2 , Todd Gisby 1 , Benjamin O'Brien 1 , Scott Walbran 1 , Emilio Calius 3
1 Biomimetics Laboratory, Auckland Bioengineering Institute, Auckland, Auckland, New Zealand, 2 Engineering Science Department, University of Auckland, Auckland New Zealand, 3 , Industrial Research Ltd., Auckland New Zealand
Show AbstractDielectric Elastomer Actuators (DEA) are popularly referred to as artificial muscles, principally on the basis that, like real muscles, they are soft and compliant and, in some configurations DEA can exceed muscle strain and strength metrics. One significant point of difference is that natural muscles can sense strain, contributing to proprioception: the ability to determine limb position. A recent advance in DEA technology is bringing such an ability closer: capacitive self-sensing. The capacitance of a DEA is related to its deformation and is critical to controlling its electromechanical stability in dynamic operation. Methods developed within our lab use pulse width modulation to both actuate and sense the DEA, and are particularly well suited to portable devices. With local self-sensing we can now look further at mimicking muscle: local control gives peripheral muscles some autonomy from the central nervous system. A good example of this is the relative autonomy of the octopus arm, able to execute complex motions with local control. Can an artificial muscle be given a fully integrated and soft self-sensing capability mimicking the natural muscle? A new development promises that this can be done in such a way that full integration with the artificial muscle can be achieved. We specifically refer to the dielectric elastomer switch, which enables sensor, logic and driver circuitry to become integral to the artificial muscle itself; based on the changes in electron conduction across a stretched elastomer electrode. A final development, closing the loop, would be linking the active artificial muscle and nerve directly to the patients own nervous system using information from EMG signals. These new artificial muscle technologies could enable reflexive prostheses, self-regulating generators, self-controlling flexible robotics, and ultimately dielectric elastomer computers.
12:15 PM - HH1.8
Introducing the Dielectric Elastomer Switch.
Benjamin O'Brien 1 , Emilio Calius 2 , Tokushu Inamura 1 , Sheng Xie 3 , Iain Anderson 1 4
1 Biomimetics Lab of the Auckland Bioengineering Institute, The University Of Auckland, Auckland New Zealand, 2 Future Materials and Structures, Industrial Research Limited, Auckland New Zealand, 3 Department of Mechanical Engineering, School of Engineering, The University Of Auckland, Auckland New Zealand, 4 Department of Engineering Science, School of Engineering, The University Of Auckland, Auckland New Zealand
Show AbstractDielectric elastomers are compliant high-voltage capacitors that provide the basis for exciting new actuator, sensor, and generator technology. As actuators (DEA) they are light, flexible, and can silently achieve large, powerful strains. They are especially suited to the creation of biomimetic arrays of actuators that work together towards common goals. Examples of potential applications include flexible robotic hearts, intestines, or cilia. There is a problem however. Conventional control of DEA requires high-voltage (typically several kilovolts) and low-current (typically several hundred microamps) external circuitry, which tends to be rigid, heavy, and expensive and thus hinders their implementation into large biomimetic arrays. In this talk we will present the new concept of the Dielectric Elastomer Switch(es) (DES). DES overcome these limitations by enabling the integration of high voltage sensor, driver and logic circuitry directly into dielectric elastomer devices. DES utilise the piezoresistivity of dielectric elastomer electrodes to control the voltage applied to DEA elements. In turn, DEA elements can control the resistivity of DES elements via the deformation fields that they induce. By patterning multiple DEA and DES elements into a device, complex circuitry can be built. We will discuss materials developed for switching and showcase two different applications, a NAND gate and an electromechanical oscillator circuit. Note that using combinations of NAND gates it is possible to build any Boolean logic circuit and that by combining Boolean logic and oscillator circuits it should be possible to create a dielectric elastomer digital computer. The end of the presentation will focus on a discussion of the limitations of the current proof-of-concept switching materials and establish requirements for new materials that will take DES out of the lab and into the real world.
12:30 PM - **HH1.9
Exciting New Opportunities for Block Copolymers as Versatile Electroactive Polymers.
Richard Spontak 1 2 , Arjun Krishnan 1 , Pruthesh Vargantwar 1 , Tushar Ghosh 3
1 Chemical & Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 Materials Science & Engineering, North Carolina State University, Raleigh, North Carolina, United States, 3 Textiles Engineering, Chemistry & Science, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractBlock copolymers have become increasingly ubiquitous in (nano)technologies requiring soft materials with, for instance, high spatial regularity at nanoscale dimensions, multiple thermo-mechanical properties and/or compatibilizing/templating attributes. Triblock and higher-order linear multiblock copolymers swollen with a midblock-selective solvent yield highly deformable networked materials with remarkable shape memory and resilience. Such characteristics are highly desirable in the design of dielectric elastomers (DEs), which exhibit lateral deformation when sandwiched between compliant electrodes and subjected to an external electric field. We have investigated a variety of DEs derived from midblock-swollen triblock copolymers varying in chemistry, composition and molecular weight. Some of the copolymer systems yield electromechanical efficiencies (i.e., the ability to convert electrical energy to mechanical work) beyond 90%, while others attain electroactuation strains close to 300%. These material systems are generally robust, facile to prepare and exhibit minimal strain hysteresis upon cycling. They can likewise exhibit substantial actuation without prestrain intended to thin specimens and reduce the potential required to achieve the field strengths capable of inducing actuation. In addition, we have found that systematic variation of the midblock-selective solvent can have a dramatic effect on the post-actuation relaxation behavior of copolymer-based DEs. Taken together, network-forming block copolymers are tremendously versatile as DE candidates and can be designed to provide application-specific electroactuation behavior over a broad performance spectrum. In the specialized case of block ionomers that possess ionic moieties in one of the blocks, the same ground-up approach can be taken to swell the ionic block with a polar solvent. In this fashion, a new generation of ionic polymer-metal composites (IPMCs) can be introduced as electroactive polymers with a well-defined and tunable nanostructure. In this case, however, mobile ionic species migrate to one side of the IPMC film during actuation and cause the film to bend. Recent results demonstrate that fully organic IPMCs produced from a sulfonated block copolymer selectively solvated with glycerol and ethylene glycol exhibit substantial electroactuation on par with or superior to those employing more conventional ionic polymers such as Nafion. Of equal importance, these IPMCs hold their deformation and do not show evidence of back-relaxation during application of the electric field.
HH2: Ferroelectric, Dielectric, and Piezoelectric Polymers
Session Chairs
Monday PM, November 29, 2010
Back Bay B (Sheraton)
2:30 PM - **HH2.1
Segmental Excitations and Gauche Bonds in the Phase Diagram of Vinylidene Fluoride – Trifluoroethylene Copolymers.
Stephen Ducharme 1
1 Physics and Astronomy, University of Nebraska, Lincoln, Nebraska, United States
Show AbstractThe phase diagram of copolymer system of vinylidene fluoride (VDF, -CH2-CF2-) with trifluoroethylene (TrFE, -CHF-CF2-) has recently been revised to include a nonpolar “antiferroelectric-like” phase in between the all-trans ferroelectric phase and the random trans-gauche paraelectric phase, at VDF compositions below 55% [1]. What is significant about this revision is the recognition that in all phases, segmental excitations are central to understanding the molecular dynamics. Whether we use as a model phase the all-trans ferroelectric phase, or the random trans-gauche paraelectric phase, it is perhaps more meaningful to think of the system as a collection of trans-segmental excitations, which are of the form GTnG, where Tn is a continuous segment of n trans bonds bounded by gauche bonds of either helicity. Then the phase diagram can be described by the distribution function N(n) of segments of length N. (For the sake of brevity, this distribution function leaves out the four possible combinations of gauche and anti-gauche terminating pairs.) The standard beta phase then has N(infinity) = 1, the paraelectric phase N(n) = 1, and only the “antiferroelectric-like” phase has a continuous distribution of N(n). This way of looking at VDF-based ferroelectric and relaxor polymers (including terpolymers) affords a new way to interpret prominent phenomena, such as the phase transitions, polarization dynamics, relaxor behavior, and nonlinear dielectric response. This work was supported by the National Science Foundation, the Department of Energy, and the Nebraska Research Initiative. [1] T. Furukawa, T. Takahashi and T. Nakajima, Current Applied Physics 10, e62-e67 (2010).
3:00 PM - HH2.2
Nanostructured Block Copolymers and Ionomers as Novel Electroactive Polymers.
Pruthesh Vargantwar 1 , Tushar Ghosh 2 , Richard Spontak 1 3
1 Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 Textile Engineering, Chemistry & Science, North Carolina State Univeristy, Raleigh, North Carolina, United States, 3 Materials Science and Engineering, North Carolina State Univeristy, Raleigh, North Carolina, United States
Show AbstractBlock copolymers (BCs) have remained at the forefront of materials research due to their versatility in applications ranging from hot-melt/pressure-sensitive adhesives and impact modifiers to compatibilizers and vibration-dampening/nanotemplating media. Of particular interest here are multiblock copolymers that are composed of two or more chemically dissimilar blocks covalently linked together. If the blocks are sufficiently incompatible and the copolymer behaves as a thermoplastic elastomer, the molecules can spontaneously self-assemble to form nanostructured materials that exhibit shape memory due to the formation of a supramolecular network. An emerging application of such BCs is in the field of electroactive polymers (EAPs), which exhibit mechanical actuation when stimulated by an external electric field. In this work, we demonstrate that BCs resolve some of the outstanding problems presently encountered in the design of two different classes of EAP actuators: dielectric elastomers (DEs) and ionic polymer metal composites (IPMCs). A new class of selectively swollen triblock copolymers is capable of yielding robust DEs that can provide high actuation strains (~110 area%), electromechanical coupling efficiencies (~80%) and energy densities (~50 KJ/m3) without requiring prestrain prior to actuation, thereby eliminating the need for the bulky frameworks currently used with conventional dielectric actuators and material problems associated with stress relaxation. In the case of IPMCs, the ionic BCs employed in this study greatly facilitate processing relative to materials such as Nafion®, which are commonly used in this class of EAPs. The unique copolymer investigated here (i) retains its mechanical integrity when highly solvated by polar solvents, (ii) demonstrates a high degree of actuation when tested in a cantilever configuration, and (iii) avoids the shortcomings of back-relaxation/overshoot within the testing conditions. The extent and dynamics of actuator movement can be controlled by varying the applied potential, and the direction of actuation can be surprisingly changed by choice of solvent. Since the morphologies and, thus, the properties of BCs can be broadly tailored through systematic variation in, for example, molecular composition and weight, this physical network approach to designer EAPs affords attractive advantages that conventional material choices do not.
3:15 PM - HH2.3
Piezoelectric Multimaterial Fibers.
Shunji Egusa 1 , Zheng Wang 1 2 , Noemie Chocat 3 , Zachary Ruff 3 , Alexander Stolyarov 1 4 , Dana Shemuly 3 , Fabien Sorin 1 3 , Peter Rakich 1 , John Joannopoulos 1 2 , Yoel Fink 1 3
1 RLE, MIT, Cambridge, Massachusetts, United States, 2 Department of Physics, MIT, Cambridge, Massachusetts, United States, 3 Department of Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, 4 School of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts, United States
Show AbstractIn recent years, a unique process has emerged that allows a multiplicity of solid materials with disparate electrical, optical, and mechanical properties to be arranged into a single fiber material. Multimaterial fibers have extended the responsivity and functionality of fibers from the traditional optical transmission domain to encompass optoelectronic properties. Applications such as fiber reflectors, thermal detectors, photodetectors, surface-emitting fiber lasers, and fiber diodes (Nature Mater. 6, 336-347, 2007) have recently been realized using this process. However multimaterial fibers similar to their traditional single-material fiber counterparts have been static devices, incapable of controllably changing their properties over a wide range of frequencies. Here we report on the design, fabrication, and characterization of fibers containing an internal crystalline non-centrosymmetric phase enabling piezoelectric functionality over extended fiber lengths (Nature Mater. 2010 accepted). A ferroelectric polymer layer of 30 µm thickness is spatially confined and electrically contacted by internal viscous electrodes and encapsulated in an insulating polymer cladding hundreds of microns in diameter. The structure is thermally drawn in its entirety from a macroscopic preform, yielding tens of meters of piezoelectric fiber. The viscous state of the fiber draw enables the departure from classical round cross sections to ones of lower symmetry thus opening interesting opportunities for shaping acoustic wave fronts. Electric fields in excess of 50V/µm are applied through the internal electrodes to the ferroelectric layer leading to effective poling of the structure. To unequivocally establish that the internal copolymer layer is macroscopically poled we adopt a two-step approach. First, we show that the internal piezoelectric modulation indeed translates to a motion of the fiber’s surface using a heterodyne optical vibrometer at kHz frequencies. Second, we proceed to an acoustic wave measurement at MHz frequencies: a water-immersion ultrasonic transducer is coupled to a fiber sample across a water tank, and frequency-domain characterizations are carried out using the fiber successively as an acoustic sensor and actuator. These measurements establish the broadband piezoelectric response and acoustic transduction capability of the fiber. The potential to modulate sophisticated optical devices is illustrated by constructing a single-fiber electrically-driven device containing a high-quality-factor Fabry-Perot optical resonator and a piezoelectric transducer.
3:30 PM - HH2.4
Electromechanical Response of Multilayered Polymer Films for High Energy Density Capacitors.
Mason Wolak 1 , James Shirk 1 , Matt Mackey 2 , Eric Baer 2 , Ann Hiltner 2
1 Optical Sciences, US Naval Research Laboratory, Washington, District of Columbia, United States, 2 Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, Ohio, United States
Show AbstractMultilayered films comprising alternating layers of polycarbonate (PC) and polyvinylidene fluoride-hexafluoropropylene (P[VDF-HFP]) show enhanced dielectric strength (EB > 750 kV/mm) and increased energy storage density (Ud~ 13.5 J/cm3) compared to monolithic PC and P[VDF-HFP] films. Failure analysis has been conducted with a Focused Ion Beam (FIB)/ Scanning Electron Microscopy (SEM) technique in which FIB is used to prepare cross-sections of a film subjected to high field. Subsequent SEM imaging provides spatially-resolved pictures of field-induced changes to the layer structure. Films driven to breakdown under a divergent field display periodic layer deformations, layer delaminations and void formations at the layer boundaries. In general, these features appear to propagate parallel to the surface and at right angles to the direction of the applied field, the direction in which a breakdown in a homogeneous film will propagate. This suggests that the layer interfaces provide a barrier to propagation of a breakdown tree across the film. SEM micrographs of films subjected to fields just below the breakdown field show evidence for buckling of the layer interfaces and for lateral flow of material within a layer. The images suggest that mechanical forces arising from field-induced compression may play a role in the steps preceding the breakdown of the multilayer materials. Furthermore, the potential importance of mechanical stress in the breakdown of similar PVDF derivatives was suggested by Claude et.al. Therefore we have measured the electro-mechanical response of PC/P[VDF-HFP] films as a function of composition (i.e. relative volume fractions) and individual layer thicknesses. A strain of approximately 0.45% is measured for 12 micron thick 32-layer 50 vol% PC / 50 vol% P[VDF-HFP] films subjected to a charge/discharge cycle with a maximum field of 500 kV/mm and a period of 3 seconds. The strain as a function of applied field can be modeled as the sum of an elastic and viscous flow component. This is consistent with the layer buckling and flow observed in the FIB/SEM images. For different composition samples, the maximum strain with this field increases with the volume fraction of P[VDF-HFP]. As the number of layers at a given composition and thickness is increased from 32 to 256 (which corresponds to roughly eight-fold decrease in layer thicknesses) both the strain and apparent flow decrease. The observed FIB/SEM evidence for mechanical changes in multilayer films subjected to a high field is confirmed by direct measurement of electromechanical effects in such films. The SEM images suggest that field-induced compression and viscous flow may play a role in influencing the breakdown mechanism and ultimately determining the dielectric strength of the multilayer dielectric composites. iJason Claude, Yingying Lu, Kun Li, and Qing Wang; Chem. Mater., 2008, 2078
3:45 PM - HH2.5
Vinylidene Fluoride Oligomers as Electroactive Coatings for Nanoparticles.
Kristin Kraemer 1 , Balamurugan Balasubramanian 1 , Ben Hage 1 , Rafal Korlacki 1 , James Takacs 2 , Lesya Kobryn 2 , David Sellmyer 1 , Stephen Ducharme 1
1 Physics and Astronomy, University of Nebrask-Lincoln, Lincoln, Nebraska, United States, 2 Chemistry, University of Nebraska-Lincoln, Lincoln, Nebraska, United States
Show AbstractFerroelectric vinylidene fluoride (VDF) oligomers are composed of finite lengths of VDF terminated on both ends by functional groups that can be tailored to offer a high flexibility of design for specific uses such as substrate and solvent compatibility. From the point of view of basic science, the oligomers are a convenient system to compare experimental results with theoretical modeling, suitable for studies of molecular crystal dynamics [1] and ferroelectricity [2]. They also have great potential for application to organic electronics due the electroactive response of the VDF monomer combined with the structural and combinatorial flexibility afforded by ready functionalization. Furthermore oligomers are easily processable and their synthesis is readily be scaled up for commercial production. We will report studies of thin film samples of pure oligomers and oligomer coated oxide (TiO2 or BaTiO3) nanoparticles made by various processing techniques including vacuum evaporation [3], spin coating, and Langmuir-Blodgett deposition. X-ray diffraction studies show that the ferroelectric phase in the evaporated films increases on increasing the evaporation temperature from 160 °C to 400 °C and becomes predominant upon post-deposition annealing at 75 °C for 2 hrs . Coating of the nanoparticles of approximately 10 nm was also performed by in situ evaporation during vacuum deposition synthesis of particles and by wet chemical replacement of ligands on commercial particles and is clearly evident from XRD, SEM and spectroscopic ellipsometry measurements. Parallel plate capacitors made of oligomers films reveal a minimum dependency on the frequency with a dielectric loss of 0.05 in the frequency range of 10-105 Hz, where the estimated dielectric constant of these films at 1 kHz is approximately 11 . Such capacitors are prototype devices for possible applications in energy storage, FETs, solar cells, and ferroelectric memories.This work was supported by the Office of Naval Research, the Department of Energy, and the Nebraska Research Initiative. [1]R. Korlacki, J. T. Johnston, J. Kim, S. Ducharme, D. W. Thompson, V. M. Fridkin, Z. Ge and James M. Takacs, J. Chem. Phys. 129, 064704 (2008).[2]K. Noda, K. Ishida, A. Kubono, T. Horiuchi, H. Yamada and K. Matsushige, Jpn. J. Appl. Phys. 39, 6358-6363 (2000).[3]B. Balasubramanian, K. L. Kraemer, N. A. Reding, Ralph Skomski, S. Ducharme, and D. J. Sellmyer, ACS Nano 4, 1893–1900 (2010)
4:30 PM - HH2.6
Microstructure and Physical Model for Observed High Dielectric Constant in CCTO-P(VDF-TrFE) Composites.
Xiaobing Shan 1 , Zhongyang Cheng 1
1 Materials Research and Education Center, Auburn University, Auburn, Alabama, United States
Show AbstractHigh dielectric constant was observed in 0-3 composites using P(VDF-TrFE) copolymer as matrix and CCCu3TiO4 (CCTO) ceramic powders as fillers [1], CCTO-P(VDF-TrFE) composites. The composites with the CCTO content from 0 to 60 vol. % were prepared and their dielectric properties including frequency dependence and temperature dependence of the dielectric constant and loss were characterized. The microstructures of the samples with the same composition but prepared with different process conditions were studied using SEM and XRD. Based on the results, the physics behind the high dielectric constant observed in the composites was discussed. It is believed that a new relaxation process is introduced in the composites and this process may be related to the interfacial layer between the polymer matrix and the CCTO powders. Reference:[1]. M. Arbatti, X.B. Shan, and Z.-Y. Cheng, Advanced Materials 19, 1369-1372 (2007).
4:45 PM - HH2.7
Effect of Thiol Functionalization on Polymer Dielectric Properties.
Leah Appelhans 1 , Shawn Dirk 1
1 Organic Materials, Sandia National Laboratory, Albuquerque, New Mexico, United States
Show AbstractThe development of functionalized polymer dielectrics based on poly(norbornene) and poly(PhONDI) (PhONDI = N-phenyl-7-oxanorbornene-5,6-dicarboximide) is presented. Functionalization of the polymer backbones by the thiol-ene reaction was examined to determine if thiol addition improved dielectric properties. Poly(norbornene) was not amenable to functionalization due to the propensity to crosslink under the reaction conditions studied. Poly(PhONDI) could be successfully functionalized, and the functionalized polymer was found to have increased breakdown strength as well as improved solution stability. Initial studies on the development of thiol-functionalized silica/poly(PhONDI) nanocomposites and their dielectric properties will also be discussed.
5:00 PM - HH2.8
Dielectric Properties of Organosilicons from First Principles.
Chenchen Wang 1 , Ramamurthy Ramprasad 1
1 , University of Connecticut, Storrs, Connecticut, United States
Show AbstractThe demand for improved high voltage, high energy density capacitors keeps increasing. A major subset of high energy density capacitors utilize polymeric materials as the dielectric, which provide several attractive properties, including ease of processability, high breakdown field and graceful failure. The present state-of-art in such capacitors is dominated by metalized biaxially oriented polypropylene (BOPP), a linear dielectric with electronic polarizability, low dielectric constant (~2.2), and respectable energy density (5 J/cc). The present work constitutes an initial step along a possible new direction to achieve high energy density, namely, one that involves organosilicon compounds. As a reference point, we note that a polymer with properties similar to Si (fast response and a dielectric constant of ~12 due to large electronic polarizability), and good dielectric strength would provide an energy density at breakdown of about 27 J/cc. While such a polymer may not be directly and immediately achievable, understanding the impact of introducing Si into the network of a base polymer such as polyethylene (PE) is useful.We consider a range of PE-based organosilicon systems in which C atoms are progressively replaced by Si. The primitive (orthorhombic) unit cell of PE contains two chains, each with two CH2 units. Successive replacement of the four C atoms of this unit cell with Si atoms resulted in systems with Si concentration of 25%, 50%, 75%, and 100% (polysilane). Density functional theory (DFT), as implemented in the Vienna ab initio simulation package (VASP), was used to optimize the structure of all organosilicon systems. Density functional perturbation theory (DFPT), also implemented in VASP, was then used to determine the elastic constant and dielectric constant tensors.The results show that both the electronic and ionic contributions to the dielectric constant of Si-substituted PE increases steadily with increasing Si content, with the total dielectric constant displaying an almost 4-fold increase along the chain axis with complete Si-substitution of all the C atoms. These increases are attributed, respectively, to enhanced σ conjugation and increased IR vibrational intensity of modes involving Si containing bonds (owing to their softness and polarity). However, concomitant with this increase, both the band gap and the Young’s modulus of these systems decrease with increasing Si content. The latter factors will be critical when designing new classes of high dielectric constant organosilicon compounds for energy storage materials.
5:15 PM - **HH2.9
Multifunctional Ferroelectric Polymers and Nanocomposites.
Qiming Zhang 1 2 , David Sheng-Guo Lu 1 , Xinyu Li 1 2 , Shan Wu 1 2 , Minren Lin 1 , Xin Zhou 1 2
1 Materials Research Institute , The Pennsylvania State University, University Park, Pennsylvania, United States, 2 Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractThe direct and efficient coupling between the electric signals and the elastic, thermal, magnetic, and optic signals in ferroelectric based electroactive polymers makes them attractive for exploiting a broad range of cross-coupling phenomena. This talk will present the recent results in our group in advancing ferroelectric polymers for actuators and sensors, ultra-capacitors, thermal management, and electro-optic applications. This talk will present recent works in these multifunctional materials for the electrocarloric cooling and energy storage devices with high energy density and low loss. We will show that by enhancing the polarization “randomness” in the ferroelectric polymers, a large electrocaloric effect can be obtained in these polymers. By properly controlling the polarization saturation in these polymers, an ultra-high energy density can be achieved. Moreover, combining these polymers with other dielectric materials can lead to novel dielectrics with high energy density and low loss.
HH3: Poster Session
Session Chairs
Tuesday AM, November 30, 2010
Exhibition Hall D (Hynes)
9:00 PM - HH3.1
Carbon-based Polymer Composites for Sensing Applications.
Jose Lobez 1 , Tim Swager 1
1 , MIT, Cambridge, Massachusetts, United States
Show AbstractNew scaffolds and molecular architectures are required to match increasing needs for more sensitive devices. In addition, organic materials are interesting for their low production cost, chemical tunability, and flexibility. We present a system based on organic molecules that undergoes degradation when interacting with a target analyte. The active component of our sensing system is a new poly(sulfone) synthesized from sulfur dioxide and olefinic monomers. This polymer is capable of generating volatile molecules after analyte sequestration, which leads to a turn-on sensing mechanism.
9:00 PM - HH3.10
Ionizing Radiation Total Dose Detectors Using Oligomer Organic Semiconductor Material and Devices.
Harshil Raval 1 , V. Ramgopal Rao 1
1 Centre of Nanoelectronics, Department of Electrical Engineering, Indian Institute of Technology, Bombay, Mumbai, Maharashtra, India
Show AbstractOrganic semiconductor materials offer various advantages like large area coverage on flexible substrates and cost effective fabrication for various organic electronic applications in circuits and sensors. Pentacene, a p-type organic semiconductor being a material with better performance characteristics compared to others, is widely used in organic circuits. Use of this oligomer organic semiconductor for detecting total dose ionizing radiation is proposed in this work. Pentacene, when exposed to ionizing radiation of γ – rays using Cobalt – 60 (60Co) radiation source, shows increase in the conductivity of the material which can be used as a sensing phenomenon for determining the total dose ionizing radiation. The change in material property was also verified using UV-visible spectrum of thin film of the material with a rising absorption peak at higher wavelength showing decrease in the distance between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the material (decreased band-gap) justifying increasing conductivity due to exposure to high energy radiation. Moreover, electric force microscopy (EFM) of samples with thin film of pentacene after irradiation have shown less electric field gradients confirming higher conductivity with increasing dose of ionizing radiation. Conductivity change in material property was also studied for its application as total dose ionizing radiation detectors using an organic semiconductor resistor sensor made up of pentacene. Change in the resistance of the sensor was measured as a measure of the ionizing radiation by electrical measurements which resulted in a sensitivity ~50 kΩ/rad for 5 krad radiation dose. Furthermore, employing this simple technique of electrical measurements for determining the ionizing radiation and to improve the sensitivity of the sensor by transistor action, an Organic Field Effect Transistor (OFET) with pentacene as an active semiconducting material was exposed to γ – radiation using 60Co source. Change in OFF current of the OFET sensor suggests a sensitivity of ~1 nA/rad for 5 krad dose of ionizing radiation. Also, changes in various parameters like ON current, OFF current, subthreshold swing, field effect mobility, shift in the threshold voltage, increasing number of interface states etc. extracted from the electrical characterizations of the irradiated OFET proved it a better choice for sensing ionizing radiation employing simple technique of electrical measurement.
9:00 PM - HH3.11
Properties of Thin Film Surface using Scale Theory.
Sergio Pithan 2 , Mirela Santos 3 , Gislayne Goncalves 1 , Rodrigo Bianchi 1 , Sukarno Ferreira 3 , Maximiliano Munford 3 , Andrea Bianchi 1
2 Department of Engineering, Federal Center for Technological Education, Araxá, Minas Gerais, Brazil, 3 Physics Department, University Federal de Viçosa, Viçosa, Minas Gerais, Brazil, 1 Physics Department, University Federal de Ouro Preto, Ouro Preto, Minas Gerais, Brazil
Show AbstractThin polymers films of polyaniline/poly(vinyl sulfonic acid) - PANI/PVS have received significant attention from researchers since these films allow the production of electronic devices, such as ammonia sensor for poultry house [1]. Some previous results show the electrical sensitivity of the system under the exposure of NH3, however the influence of surface morphology (roughness) in electrical conductivity is not well established. In this work we have been investigating the PANI/PVS surface formation using atomic force microscopy (AFM) and scale theory [2], described by statistical methods that take into account the time involved in the formation of the surface as wellas the scale on which the morphology is observed.The PANI/PVS films were deposited onto glass substrate by layer by layer (LbL) technique, using 0.39mg/ml of PANI, which allows precise control over film thickness and molecular architecture. The multilayer was monitored at each deposition step by UV-VIS spectroscopy, a quantitative analysis of the surface roughness is of extreme importance in investigating the adsorption phenomena of NH3 and in controlling the final surface features. As these films are obtained by LbL, a quantitative analysis of the surface topography is being formed by AFM image analysis.The images used for analysis are obtained by atomic force microscope AFM in a scan window of 2×2μm2 from LbL PANI/PVS films considering 30 minutes for immersion time for 1, 5 and 10 bilayers. The films present a linear growth with visible increase in height as the number of layers increases. The dynamic scaling theory was employed to obtain the roughness exponents [2]. The roughness exponents is determined by a log W versus log L plot, where W is the roughness and L is the size of the scan window. Previous results show roughness for 30 minutes and 30 seconds regarding the immersion times, it can be seen that roughness increases 30 minutes of immersion time and decreases for 30 seconds as the number of bilayers increases. Such results indicate different behavior for PANI/PVS immersion times. Some models have been investigated to describe interface formation, as well as a more detailed experimental approach varying the immersion time. Indeed, there has been evidence that polymer adsorption to form nanostructured films are governed by properties at the mesoscale due to aggregation in solution. This research was supported by Fapemig, Capes and CNPq and CNPq/INEO.References[1] M. C. Santos et. al., Polímeros, (2010), in press.[2] A. L. Barabasi et. al., Fractal Concepts in Surface Growth, Cambridge University Press(1995).
9:00 PM - HH3.12
Effects of Polymer Degradation on the Filtration Properties of a Fibrous Mat.
Jigneshkumar Patel 1 , Onur Kas 1
1 , Millipore Corporation, Beford, Massachusetts, United States
Show AbstractPolyamides are highly chemical resistant due to their intermolecular H-bonding capabilities. They can only be dissolved in highly acidic solutions, like formic acid, or highly fluorinated solutions, like hexafluoroisopropanol, in which they are susceptible to degradation. Degradation takes place even as one prepares a polymer solution from a dry pellet form. Therefore solution preparation conditions (temperature, time and solvent formulation) play a big role in the final molecular weight of the polymer. In this systematic study various temperature, time and solvent formulations and initial polyamide molecular weights were used. The resulting degradation amounts were characterized by viscosity and molecular weight measurements via a viscometer and gel permeation chromatography (GPC), respectively. Degradation at room temperature over prolonged periods of times was also investigated. Out of these solutions fibrous mats were produced and their filtration properties (bubble point, permeability) were measured. It was found that solution properties like conductivity and viscosity have a substantial impact on mat properties. Final polymer molecular weight in solution dictates viscosity and therefore fiber formation process determining the integrity of the final filter mat.
9:00 PM - HH3.13
Development of Thin Film Transistors Using Conjugated Polymers and Polymeric Electrolytes.
Giovani Gozzi 1 , Roberto Faria 1 , Lucas Fugikawa Santos 2
1 Physics, Instituto de Fisica de Sao Carlos - USP, Sao Carlos, SP, Brazil, 2 Physics, UNESP - Univ Estadual Paulista, Sao Jose do Rio Preto, SP, Brazil
Show AbstractOrganic electronic devices comprising conjugated polymers and ionic conducting polymers, have been fabricated in structures similar to organic field-effect transistors (OFETs). Polymeric blends of polyfluorene derivatives and ionic transporting polymers, as poly(ethylene oxide), complexed with different alkaline metals salts, have been used as the active layer of the fabricated devices. The purpose of using such blends is to reduce the injection barriers for electronic carriers through the electrodes, giving rise to the formation of an electrochemically doped region in the transistor channel, which doping level can be controlled by the bias applied to the gate electrode. Since electrochemical doping can occur by oxidation/reduction of the conjugated polymer, such devices are expected to present bipolar transport and can be used in CMOS-type (complementary metal oxide semicondutor) inverter devices. The devices have been electrically characterized by d.c. current-voltage measurements, by the characteristic transistor transfer curves and by electric impedance spectroscopy in the frequency domain. Particularly, impedance spectroscopy technique has been used in order to distinguish the contribution of each type of charge carriers (electronic and ionic) to the electrical properties of the devices, allowing the determination of the parameters for improved device performance.
9:00 PM - HH3.14
The Study about the Control of Defect Factors to Improve Properties of P(VDF-TeFE) Thin Film.
Jong-Hyeon Jeong 1 , Daiki Terashima 1 , Chiharu Kimura 1 , Hidemitsu Aoki 1
1 Department of Electrical Electronic and Information Engineering, Osaka University, Suita, Osaka, Japan
Show Abstract In order to study about the fabrication of a micro-generator based on MEMS technology, we have carried out the study about a film formation of piezoelectric polymer and an improvement of properties by control of defect factors. In this study, the procedures is classified by two category as following; first, an improvement of physical properties in a coating process through a control of humidity. The other is an improvement of chemical properties in an annealing process through a control of temperature and an intensity of electric field which is applied to the film in the process. The film which is formed in the optimized condition has almost same electrical properties with bulk-state of the polymer. In various energy harvesting technologies, we have focused on human voice to extend the operating life-time of portable electronic devices. Since a human voice has irregular frequency and energy as an acoustic wave, we have studied about the fabrication of a membrane-type micro-generator which has low resonant frequency using a piezoelectric polymer. Thus, we have selected P(VDF-TeFE) (Poly vinylidene fluoride and tetrafluoroethylene) which is the same with PVDF as a copolymer in all aspects. Since a stretching method is impossible to apply to MEMS process, a spin-coating and annealing process was carried out to form the film. However, this coating method caused low uniformity of film surface and falling-off in electrical properties by pin-hole on a film surface. Through an annealing process at a temperature higher than Curie point, the surface uniformity is improved considerably, but a polarization of the film is fallen seriously. In the film forming process, the external variables which have a bad influence on formation of the film is as following; the temperature and humidity on a coating process, the intensity of an electric field and humidity on an annealing process. Methyl-ethyl-ketone (MEK) and n, n-dimethylacetamide (DMAc) were used as a solvent to cast the polymer granule. Single and mixed solutions were prepared as a coating solution; single solution was made up only MEK and mixed solution was made up MEK and DMAc. To control humidity during the coating process, spin-coating process was carried out at the humidity was less than 10%. Also, the annealing process was carried out at 195 °C in a vacuum chamber. The electric field was applied by 0, 0.5, 1 and 2 MV/m for 2 mm distance between electrodes during the annealing process. According to measured data, we have compared quantitatively the ratio of each bond in single and mixed solution with an intensity of the electric field. It is found that the electric field and humidity affect the properties of the film during the forming process. In our result, we found that there is a suitable intensity of an electric field to have a decisive effect on the properties of the film. In addition, the lower humidity during the processes, the better a surface state of the film is stable.
9:00 PM - HH3.15
New Insights into Solvated Block Copolymer Networks as Nanostructured Dielectric Elastomers.
Arjun Krishnan 1 , Pruthesh Vargantwar 1 , Tushar Ghosh 2 , Richard Spontak 1 3
1 Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 Textile Engineering, Chemistry & Science, North Carolina State University, Raleigh, North Carolina, United States, 3 Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractBlock copolymers are macromolecules consisting of long, contiguous sequences of chemically dissimilar repeat units that are covalently linked to permit molecular self-assembly into a variety of nanostructures. Selective midblock solvation of styrenic triblock copolymers yields physically networked materials possessing shape memory even after significant strain deformation. For this reason, such materials are ideal for use as dielectric elastomers (DEs), which convert electrical energy into mechanical work by changing dimensions upon application of an electric field. In this case, a DE film is sandwiched between compliant electrodes that generate a normal Maxwell stress, which compresses the film and promotes transverse strain. Our previous studies have demonstrated that DEs derived from poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) triblock copolymers swollen with an aliphatic mineral oil exhibit the same electroactuation strain behavior and blocking force as human muscle with electromechanical efficiencies exceeding 90% and without much cycling hysteresis. Although numerous studies have investigated DEs, substantial variation in reported properties persists. We have observed that, although specimen thickness is taken into account in calculating the electric field, the magnitude of the unstrained specimen thickness influences actuation behavior due to the initial extent of physical or chemical network formation. In addition, we find that the electromechanical modulus, which constitutes a useful metric of actuator performance, obeys the same polymer scaling behavior as the mechanical compressive modulus. To alter the time response of the actuator, we have developed DEs based on SEBS copolymers and a midblock-selective cosolvent composed of mineral oil and a glassy tackifying resin. The DEs prepared from these ternary systems exhibit systematically controllable relaxation behavior and energy densities in excess of 8 MJ/m3. Dynamic rheological analysis of these systems reveals that frequency spectra acquired at different concentrations can be smoothly shifted to yield master curves, thereby confirming the existence of time-composition equivalence. In the same spirit as time-temperature superpositioning (tTS), time-composition superpositioning (tCS) permits prediction of mechanical properties at very long or short timescales by changing a convenient system variable. Lastly, DE actuation involves transverse stretching, which can be approximated as biaxial strain. To discern the effect of biaxial strain on copolymer nanostructure, small-angle x-ray scattering (SAXS) has been used to probe the nanostructural evolution of films strained up to 300%. While the form factor from the glassy styrenic domains verifies that the shape of the domains is nearly independent of strain, analysis of the structure factor by a modified Percus-Yevick model reveals that the normally repulsive domains develop an attractive potential upon biaxial strain.
9:00 PM - HH3.16
Multi-layered PVDF Systems for Enhanced Energy Harvesting and Sensing.
Jennifer Jones 1 , Roberto Aga 1 , Richard Mu 1
1 Physics, Fisk University, Nashville, Tennessee, United States
Show AbstractPolyvinylidene fluoride (PVDF) is a well known piezoelectric polymer with applications in energy harvesting and sensing. The output voltage, current generation and structural rigidity of PVDF piezoelectric devices can be enhanced through the development of multilayered structures. We are developing a multilayered piezoelectric system which consists of alternating layers of thin film PVDF and electrodes for efficient ambient energy harvesting and piezoelectric sensing. The multilayered systems under investigation can be fabricated via a co-extrusion process. To determine the piezoelectric effect of these systems characterization techniques are developed consisting of acoustic excitation, cantilever based resonant oscillation, and forced constant amplitude vibration. These techniques provide complimentary testing platforms with frequencies ranging from 10Hz - 10kHz, energy harvesting efficiency for real world comparison, and a quantitative evaluation for the piezoelectric coefficient from the measured amplitude of deflection. The transient output signals were measured and analyzed with the help of an oscilloscope and a spectrum analyzer. A simple theoretical calculation has also been carried out to predict the multilayer device performance and critical parameters for device optimization. Our results show that an increase in the output voltage has been observed for multilayered systems versus single layered. From the material design standpoint, the output voltage is very sensitive to the quality of the inserted conducting flexible electrodes.
9:00 PM - HH3.17
Synthesis of Polymer Ferroelectric Islands Without Long-range Order.
Yoonyoung Choi 1 , Seungbum Hong 2 , Jongin Hong 1 , Moonkyu Park 1 , Hanwook Song 3 , Kwangsoo No 1
1 , Korea advanced institute of science and technology, Daejeon Korea (the Republic of), 2 , Argonne National Laboratory, Lemont, Illinois, United States, 3 , Korea Research Institute of Standard and Science, Daejeon Korea (the Republic of)
Show AbstractFerroelectric polymers are great candidate materials for piezoelectric energy harvesting devices because they are piezoelectric, cheap, lightweight, flexible and easily processed. Among them, poly(vinylidene fluoride-trifluoroethylene), P(VDF-TrFE), has stable ferroelectric β-phase at room temperature that exhibits strong piezoelectric properties, which is suitable for various applications including transducers, actuators, sensors and nonvolatile memory devices.We have previously published our work on optimizing the annealing temperature of PVDF-TrFE (75:25) thin films to maximize stable ferroelectric β-phase and correlate its content with local piezoelectric properties obtained by piezoresponse force microscopy (PFM). In an attempt to quantitatively analyze the relationship between crystallinity, fraction of β-phase and local piezoresponse, we found that when annealed above the melting temperature and quenched to room temperature, micron-sized ferroelectric islands formed on the substrate, which showed no crystalline peak in x-ray diffraction pattern.To reproduce the result and compare it with that of continuous crystalline film, P(VDF-TrFE) powders in a molar ratio of 75/25 were dissolved in methyl ethyl ketone (MEK). Subsequently polymeric films were deposited on the Au/Ti/Si substrates by a spin-coating technique and annealed at 135°C (film) and 150°C (islands) for 2 hours. To confirm the absence of long-range order and existence of ferroelectricity in P(VDF-TrFE) islands, they were analyzed by Fourier Transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Transmission electron microscopy (TEM), atomic force microscopy (AFM) and piezoresponse force microscopy (PFM).
9:00 PM - HH3.19
Detrapping Effects on the External, the Conduction and the Displacement Currents in LDPE Polyethylene Film.
Imed Boukhris 1 , Ezzeddine Belgaroui 1 , Ali Kallel 1
1 Physics, Faculty of sciences of Sfax_Laboratory of ceramics, composites and polymers, Sfax Tunisia
Show AbstractWe present a model for bipolar charge transport in low density polyethylene films under dc applied voltage. Theoretically, this model is based on trapping-detrapping and recombination mechanisms. The physical equations of the model are resolved by very accurate numerical techniques. In this work, we are interested especially in examining the detrapping effects. In fact, these effects are shown on the model results that are carried out for the net charge density, the electric field, the mobile and the trapped carriers, the recombination rates as well as the current densities.
9:00 PM - HH3.2
Compact High Temperature Polymer Film Capacitors for Power Inverters in Hybrid Electric Vehicles.
Shihai Zhang 1 , Chen Zou 1 , Xin Zhou 1 , Douglas Kushner 1 , Qiming Zhang 1
1 , Strategic Polymer Sciences, Inc., State College, Pennsylvania, United States
Show AbstractPower electronics are a key technology for hybrid and plug-in electric drive vehicles (EDV) and represent 20% of the material costs. DC bus capacitors are one of the critical components in EV power inverters and they can occupy ~35% of the inverter volume, contribute to ~23% of the weight, and add ~25% of the cost. Current polypropylene (PP) film capacitors have dielectric constant K of 2.2 and temperature stability lower than 105 degree C. We recently developed a modified polytetrafluoroethylene (PTFE) which combines high dielectric constant, low dielectric loss, low leakage current, high dielectric breakdown strength, and high temperature stability. The modified PTFE capacitor film also has graceful failure feature which is critical to applications demanding high reliability and long lifetime. The thermoplastic nature of the modified PTFE ensures that they can be processed into thin capacitor film with thickness of 2 microns to 5 microns using inexpensive melt extrusion and biaxial orientation process. In this report, extensive high voltage test results of the novel capacitor film will be presented.The advanced DC bus capacitors can also be used in power electronics in photovoltaics, wind turbine generators, and other industrial applications, where they will facilitate the more efficient utilization of electrical energy.
9:00 PM - HH3.20
High Energy Efficiency Capacitors Based on Polar-fluoropolymer Blends.
Shan Wu 1 2 , Minren Lin 2 , Qiming Zhang 1 2 3
1 Electrical Engineering Department, The Pennsylvania State University, University Park, Pennsylvania, United States, 2 Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania, United States, 3 Materials Science and Engineering Department, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractThis talk presents recent advances in developing high energy density polymer capacitors with low loss. In order to reduce the dielectric loss while maintaining high energy density in the P(VDF-HFP) and P(VDF-CTFE) based polymers, a polymer blend approach was investigated. We show that by blending P(VDF-CTFE) with a low loss polymer can lead to marked improvement in the loss of dielectric films. Blends films with proportion from 20% to 50% of the low loss material are examined to find a balance between dielectric constant and the loss. In addition, crosslink of the two materials is used to further improve the dielectric performance of the blends. The results indicate that blends have an excellent performance: relatively high dielectric constant which is around 6~7, low loss about 0.01 at 1 KHZ. And for the crosslink films, the energy efficiency can be even as high as 95.2% at a high field of 300 MV/m.
9:00 PM - HH3.21
Anion Exchange of Oligomeric Electrolytes as Novel Gel-forming Materials: Tuning of Solubility and Gelation Ability.
Masaru Yoshida 1 , Nagatoshi Koumura 2 , Hajime Matsumoto 3
1 Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan, 2 Photonics Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan, 3 Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology, Ikeda, Osaka, Japan
Show AbstractRecently we reported novel oligomeric electrolyte as a multi-functional gel-forming material. To tune the miscibility of the gel-forming oligomeric electrolyte for various solvents, we examined the anion exchange reactions using suitable ammonium salts or alkali-metal ones. Nine oligomeric electrolytes with different anions were obtained in high yields by the reactions. The solubility of these oligomeric electrolytes in organic solvents was carefully tested. Although the starting material with chloride as a counter anion was not soluble in any organic solvents, the excellent miscibility and the gelation ability of the oligomeric electrolytes with different anions were accordingly observed using dipolar protophilic and aprotic solvents, such as N,N-dimethylformamide (DMF), dimethylsulfoxide (DMSO) and N,N-dimethylacetamide (DMA). In addition, the ionogels based on the aliphatic ionic liquids were readily formed using the oligomer with bis(trifluoromethanesulfonyl)amide anion at a 40 g/L concentration. It is remarkable that the ionic conductivity of those ionogels is almost identical with those of neat ionic liquids, in spite of the significant increase of the apparent viscosity. This study shows a novel and convenient approach for the gel-forming materials for multi-solvents.
9:00 PM - HH3.22
Development of Polymeric Concrete from Recycled PET.
Martha Lilia Dominguez Patino 1 , Alma Delia Rodriguez Martinez 2
1 Facultad de Ciencias Quimicas e Ingeneria, Universidad Autonoma Del Estado de Morelos, Cuernavaca, Morelos, Mexico, 2 Posgrado en Ingenerria y Ciencias Aplicadas, Universidad Autonoma Del Estado De Morelos, Cuernavaca, Morelos, Mexico
Show AbstractAs we know the polymer concrete composite posses a unique combination of properties that depend upon the formulation, also there are studies that reviewed variations in polyester polymer concrete mixture components that affected the properties, The effect of resin content aggregates, fibers and coupling agents were critically reviewed, it was found that the polymer content varied from 12 to 14 % (W/W) (Garas and Vipulanandan, 2003).Every day we generate solid waste and we must to answer to the question How can we reduced the use of virgin raw material and increase the use of recycle materials? In general, the people do not recycle the bottles of polyethylene terephthalate (PET) that during more of 50 years in decomposition and more if they are buried. The objective of this work is to take advantage and revalorize the urban solid waste for development the new materials for constructions. This kind of activities allows reducing the environment impact and designing green process.The process consists of two steps. In the first step we use recycled PET as raw material. In this step we obtain a PET with physical and chemical properties identical to the original material. In the second step we mix a polyester resin, flakes of PET (pure and recycled) and carbonate of calcium. The polymeric concrete obtained has satisfactory properties for construction.
9:00 PM - HH3.23
Investigation of Three Phase Percolative PZT-Epoxy-aluminum Composites for Structural Health Monitoring and Energy Harvesting Applications.
Sankha Banerjee 1 , Kimberly Cook-Chennault 1 2
1 Mechanical and Aerospace Engineering, Rutgers, The State University of New Jersey, Piscataway, New Jersey, United States, 2 , Center for Advanced Energy Systems, Piscataway, New Jersey, United States
Show AbstractNew composite materials and devices are been investigated by researchers in the field of structural health monitoring (SHM) of civil and mechanical structures and energy harvesting applications. The criteria that govern the applicability of these types of devices are their sensitivity and durability, which depend on properties such as the dielectric constant, piezoelectric strain coefficient, dielectric loss and mechanical strength. The present work investigates the role of Aluminum and PZT inclusions uniformly distributed in an epoxy matrix to fabricate composites with high dielectric and piezoelectric strain coefficients. These composites are fabricated by a two step mixing procedure which includes 1) mixing of PZT and epoxy mixture and 2) dispersion of Aluminum particles in ethanol. The mixture is then cured via use of a curing agent at a temperature of 75 degree C for 8 hours. The composite shows an increase dielectric and piezoelectric properties with an increase in volume fraction of both PZT and Aluminum particles. Above a certain volume fraction of the conductive Aluminum component the dielectric loss of the composite increases rapidly which is attributed to the phenomenon of percolation. This renders the composite inapplicable in the above mentioned uses. The percolation threshold and percolation limit for the above composite is also determined. A comparative study of the change in material properties and percolation characteristics with variation of Aluminum volume fraction is demonstrated here. The results from the experiments are also compared with an analytical model developed for predicting the dielectric and d33 piezoelectric strain coefficients of 0-3-0 composites.Key Words: SHM, composite, dielectric, piezoelectric, Aluminum, PZT
9:00 PM - HH3.24
Theoretical and Experimental Investigations of Polymer Photodegradation Process to the Viability Analysis of Radiation Sensor for Neonatal Phototherapy.
Claudia Vasconcelos 1 , Giovana Ferreira 1 , Marcelo Flores 2 , Pedro Autreto 2 , Douglas Galvao 2 , Rodrigo Bianchi 1
1 Department of Physics, Federal University of Ouro Preto, Ouro Preto, MG, Brazil, 2 Physics Institute, University of Campinas, Campinas, São Paulo, Brazil
Show AbstractOptical properties of luminescent polymers have been studied since the first report of electroluminescence in poly(p-phenylenevinylene) (PPV) in 1990. These materials are commonly employed in light-emitting displays because of their good processability, lightweight and higher luminance with low power consumption. However, the performance of these devices is limited by high susceptible to photodegradation processes which dramatically reduce the quantum efficiency and the lifetime of their devices. The changes in photoluminescence and absorbance spectra caused by visible radiation reflects the possibility to design and develop sensors where the effects of visible radiation on the optical properties of luminescent polymers are more important than improving the luminance and lifetime of the light-emitting devices made from them. Moreover visible sensors are desired especially in medical applications where blue-light phototherapy is used, for example, in neonatal disease treatments where exists a strong relationship between the rate of decline in serum bilirubin level of infant’s skin and the intensity and spectral qualities of the light source, as well as the distance between the light source and the neonates. In this work we investigated the changes on the optical behavior of poly(2-metoxy-5(2’-ethylhexyloxy)-p-phenylenevinylene) (MEH-PPV) systems under the effect of blue-light radiation (460 nm focus, 40 µW/cm2). We have also developed a model for MEH-PPV photodegradation based on structural changes of PPV derivatives oligomers in vacuum, in chloroform and in toluene solvents. It is observed changes from orange-red to yellow clearly on polymer systems, while its peak position emission shifts from orange-red to blue and decrease in intensity with increasing radiation exposure time. Our theoretical calculations were carried out on degradation structural models in which the effects the conjugation length. The results indicated that the inclusion of oxygen within the polymeric chain can produce significant blue shift in the absorption spectra, with associated decreasing in the intensity of the absorption spectra and in excellent agreement with the available experimental data. These results are very useful for maximizing the sensibility and specificity of a MEH-PPV as active material for blue-light sensors applied in neonatal phototherapy. Work supported by INEO/CNPq, CNPq, FAPEMIG, CAPES and FAPESP.[1] DE VASCONCELOS, C. K. B., BIANCHI, R.F. Sens. and Act. B, Chem. 143, 30 (2009).[2] FERREIRA, G. R., DE VASCONCELOS, C. K. B., BIANCHI, R. F. Med. Phys. 36, 642 (2009).[3] AUTRETO, P. A. S., DE VASCONCELOS, C. K. B., FLORES, M. Z. S., GALVAO, D. S., BIANCHI, R. F. Mat. Res. Soc. Symp. Proc.1, 1133-AA07-14 (2009).
9:00 PM - HH3.25
Polymeric Based Waveguides for Optical Biosensor and Wavelength Conversion.
Mike do Vale 1 , Leni Akcelrud 3 , Francisco Eduardo Guimaraes 2
1 IFSC, Universidade de São Paulo - USP, São Carlos, São Paulo, Brazil, 3 Departamento de Química, Universidade Federal do Paraná, Cutitiba, Paraná, Brazil, 2 IFSC, Universidade de São Paulo - USP, São Carlos, São Paulo, Brazil
Show AbstractThe main goal of this work is the production and the study of planar wave guides based on a polymeric blend composed of light emitting polymers embedded in a transparent polymetacrilate (PMMA) matrix. The function of these light emitting polymers is to absorb a broad spectrum of light and re-emit it along the wave guide. Interesting features arise from the luminescent process along these planar systems. The devices were studied in terms of its absorption, emission and excitation characteristics. Planar wave guides were formed by using blends with different luminescent polymers embedded in a PMMA matrix. Films of these materials dissolved in toluene were deposited by casting the polymethacrylate solution on a glass substrate containing a reflective aluminum layer. Using this configuration, the incident excitation light is coupled to the wave guide by its absorption and then re-emitted by the luminescent polymers. These wave guides show a light emission spectrum with characteristics similar to the Fabri-Perot cavity, where very narrow peaks and highly polarized emission in both TE and TM modes were observed. In addition, the emission is strongly dependent on its geometry and the effective refraction index. In other hand, thicker polymeric guides (30 μm) were used as luminescence solar converters (LSCs). The optimal concentration of conjugated polymers has to be very low in order to avoid the formation of aggregates since high PMMA concentrations have to be used in the LSC preparation. The study of such LSCs was carried out by measuring the lateral and the normal emissions of the guide. The total polymeric luminescence is fully converted to light of low wavelength for the case of lateral emission. This process does not depend on the excitation wavelength. The conversion efficiency was increased by evaporating metals on one planar face of the LSC. In this structure, light is absorbed and then converted to a shorter wavelength with high spectral pureness through re-absorption, relaxation and re-emission processes occurring along the LSC plane. The conversion efficiency and the losses along the converter were studied as a function of the polymeric concentration. In order to optimize these structures, a full understand the process of energy transfer and photon leakage through the interfaces for angles smaller than the critical angle (θc=sen-1(1/n)) is necessary for using LSCs as devices.
9:00 PM - HH3.26
Synthesis, Characterization and Photovoltaic Properties of a Series of Benzo[1,2-b:4,5-b’]dithiophene-based Conjugated Polymers for Solar Cell Applications.
Christopher MacNeill 1 , Robert Coffin 2 , Eric Peterson 2 , David Carroll 2 , Ronald Noftle 1
1 Department of Chemistry, Wake Forest University, Winston-Salem, North Carolina, United States, 2 Center for Nanotechnology and Molecular Materials, Department of Physics, Wake Forest University, Winston-Salem, North Carolina, United States
Show AbstractAt the rate of present consumption of fossil fuels and the strain it puts on the environment, it is only a matter of time before we have to rely on other energy sources. Harvesting energy from sunlight is widely regarded as the approach to alternative energy production in the future. Researchers are trying to determine the easiest and most cost-efficient way to convert light into electricity using solar cell devices. Recently, some attention has been directed toward using benzo[1,2-b:4,5-b’]dithiophene (BDT)-based monomers as electron-donating components in polymer solar cells. This is due to the ease of functionalization of certain positions on the BDT backbone in order to tune the electronic properties of the polymer. The structure-property relationship between side chains on low band gap BDT-based polymer backbones has yet to be investigated in great detail. Varying the alkoxy side chain on the backbone of BDT may allow for greater solubility and in-turn greater solution processability, higher molecular weight and better device characteristics. Here, we report the synthesis and characterization of a series of electron-donating monomers based on benzo[1,2-b:4,5-b’]dithiophene with alkoxy side-chains. Co-polymerization with an electron-withdrawing monomer will allow us to adjust the band-gap of the polymers so we can achieve high power conversion efficiencies (PCE). The photovoltaic properties of the polymers are also discussed.
9:00 PM - HH3.27
Influence of the pH on the Surface and Optical Properties of the Thin Film of Polyaniline Polyethylene Teraphthalate Composite. The AFM and Spectroscopies Studies.
Rafaella T Paschoalin 1 2 , Paulo S. P. Herrmann 1 , Clarice Steffens 1 2 , Alexandra Manzolli 1
1 National Laboratory for Nanotechnology in Agribusiness , Embrapa Agricultural Instrumentation, Sao Carlos, Sao Paulo, Brazil, 2 Biotechnology Graduated Program, UFSCar , Sao Carlos, Sao Paulo, Brazil
Show AbstractIn this work we are using atomic force microscopy (AFM) and spectroscopies techniques to investigate the influence of pH of the solution in the surface morphology and optical response of the PANI in the emeraldine oxidation state composite with polyethylene teraphthalate (PET). The PET/PANI strip was developed using in-situ chemical polymerization, using polyaniline in the emeraldine oxidation state, doped with HCL, used to measure the pH of solution. The absorption of UV-Vis spectra was used to evaluate the optical response to pH change of natural water. The strip showed a reversible color change upon variation of the pH. The shift is characteristic of dedoping of polyaniline, similarly to that which occurs for PANI dedoped by other methods. The pH ranges used to calibrate the optical sensor were from 2.0 to 12.0. With the UV-Vis-NIR spectroscopy was possible to observe the influence of the pH at the molecular level of the PET/PANI composite, that showing a molecular coil conformation.The repeat unit of PANI is composed of three phenylene rings that present an aromatic character, which was investigated using the Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR), and one another ring adopting a quinoid character. Since the extent of electron delocalization and conjugation is reflected by the behavior of bond-length alternation along the backbone of the conjugated polymers.It can be observed that the differences between the PANI/ PET depoded and doped are related mainly to the effects of interaction between rings benzenoid/quinoid polymers with the solution. In basic pH bands showed further enlargement to be due to interaction of the OH group.From the AFM images, the Ra and rms roughness values and the average height were obtained and calculated. The roughness showing different behaviour in acid and basic regime.The hypothesis is that hydrogen bond play a key role, and could be explain the modification in the morphology.
9:00 PM - HH3.28
Surface Plasmon Enhanced SP-exciton Coupling of Conjugated Polymer Using Ag Nanostructures.
Kwan Hyun Cho 1 , Chung Sock Choi 1 , Seong Min Lee 1 , Kyung Cheol Choi 1
1 Department of Electrical Engineering, KAIST, Daejeon Korea (the Republic of)
Show AbstractConjugated polymer-based optoelectronic devices such as polymer light-emitting diodes (PLEDs), organic semiconductors, and organic solar cells [1-3], have been the subject of much interests owing to their inexpensive fabrication process and usefulness when applied to flexible devices. In addition, the light enhancement of fluorophores due to excitation of the surface plasmon resonance using nanostructues represents one of the most attractive fields related to plasmonic devices [4]. This study demonstrate surface plasmon enhanced SP-exciton coupling of conjugated polymer in PLEDs through Ag nanostructures fabricated via a simple and effective method involving thermal evaporation.Localized surface plasmon resonance (LSPR) characteristics were controlled according to the size and density of randomly distributed nanoparticles. LSPR peak wavelengths were red-shifted as size and density of the Ag nanoparticles increased [5]. Propagating surface plasmons (PSP) were controlled using connected islandized films by varying the evaporation time. Ag nanostructures were positioned between PEDOT:PSS and an ITO substrate. In the connected islandized Ag films, the absorbance spectra of the ITO substrate/Ag nanostructure decreased due to the transition from localized surface plasmon (LSP) to propagating surface plasmon (PSP). However, the absorbance spectra of the ITO substrate/Ag nanostructrue/PEDOT:PSS/MEH-PPV increased due to the strong interactions between the surface plasmons (SPs) and the exciton in the MEH-PPV.Photoluminescence (PL) values were measured on both directions of the emitting layer side and on the ITO substrate side simultaneously, while excitation light of 500 nm was incident at the emitting layer side. The PL emission in the emitting layer side was increased as the Ag nanostructures become film-like. The PL results of the ITO substrate side showed a peak value for a sample having connected islandized nanostructures. This peak value arises due to the relative strong SP-exciton coupling in the connected islandized films rather than in isolated nanoparticle structure, and due to the increase in the transmittance with the transition from LSP to PSP resonance.From these results, the performance of PLEDs using connected islandized Ag nanostructues can be enhanced due to the strong SP-exciton coupling. References[1]R.H. Friend, R.W. Gymer, A.B. Holmes, J.H. Burroughes, R.N. Marks, C. Taliani, D.D.C. Bradley, D.A. Dos Santos, J.L. Bredas, and M. Lögdlun,” Nature, vol. 397, 1999, pp. 121–128.[2]S. Günes, H. Neugebauer, and N.S. Sariciftci, Chem. Rev, vol. 107, 2007, pp. 1324–1338.[3]N.C. Greenham, X. Peng, and A.P. Alivisatos, Physical Review B, vol. 54, 1996, pp. 17628–17637.[4]K. Okamoto, I. Niki, A. Shvartser, Y. Narukawa, T. Mukai, and A. Scherer, Nature materials, vol. 3, 2004, pp. 601–605.[5]G. Xu, M. Tazawa, P. Jin, S. Nakao, and K. Yoshimura, Applied Physics Letters, vol. 82, 2003, p. 3811.
9:00 PM - HH3.29
Organic-Inorganic Multi Barrier Encapsulation for Long Lifetime of OLED.
Yun Cheol Han 1 , Kyung Ho Jung 2 , Kyung Cheol Choi 1 , Byeong Soo Bae 2
1 electrical engineering, KAIST, Daejeon Korea (the Republic of), 2 material science, KAIST, daejeon Korea (the Republic of)
Show AbstractOLEDs have great potential for use in next generation displays. However, the organic materials used in OLED are very sensitive to oxygen and water vapor. The organic-inorganic multi barrier is a promising method for high performance flexible substrates. Also, multi barriers play an important role as passivation layers.The characteristics of organic-inorganic multi barriers were investigated. Sol-gel hybrimer and MgO were used as organic and inorganic materials, respectively. The water vapor transmission rate (WVTR) was measured so far around 10-5 g/m2day by Ca test. [1] The average transmittance of the multi barriers was measured at 80 % in the visible region (350 nm ~ 580 nm). The lifetime was estimated for the constant current driving with initial luminance L0 = 1000 cd/m2 at the ambient. [2] The half life of the OLED device encapsulated with multi barriers was compared with that of a glass-encapsulated device. We have fabricated an OLED on a plasma-treated ITO glass substrate, doped with DCJTB. Following the fabrication, sol-gel hybrimer was spin-coated on the top of the OLED to a depth of 1 μm, and was cured by UV. Also, 100 nm MgO was deposited by electron beam evaporator. Organic-inorganic layers were stacked alternatively. The organic-inorganic multi barrier coating method was an effective way to prevent the transmission of the oxygen and moisture. Because of the alternating layers, the path of the transmission was longer. Increasing the number of multi layers, we were able to obtain low WVTR. Also, the first organic layer functions as a buffer layer during the MgO deposition process. We were able to encapsulate the OLED without dark spots. In summary, a Sol-gel hybrimer / MgO multi layer has a low WVTR of around 10-5 g/m2day and 80 % average transmittance. This multi barrier is useful for thin-film passivation or as a flexible display substrate.REFERENCE[1] R. Paetzold, A. Winnacker, D. Henseler, V. Cesari and K. Heuser, Review of Scientific Instruments, 74, 5147-5150 (2004).[2] C. Fery, B. Racine, D. Vaufrey, H. Doyeux, and S. Cina, Applied Physics Letter, 87, 213502 (2005).
9:00 PM - HH3.3
Degradation of PDHFPPV and Its Possible Application in Radiation Sensor.
Giovana Ferreira 1 , Eduardo de Azevedo 2 , Leni Akcelrud 3 , Rodrigo Bianchi 1
1 Department of Physics, Federal University of Ouro Preto, Ouro Preto, MG, Brazil, 2 , Physics Institute of São Carlos, São Carlos, São Carlos, Brazil, 3 , Federal University of Paraná, Curitiba, Paraná, Brazil
Show AbstractThe study and application of these materials in emitting devices, photovoltaic cells and, more recently, radiation sensors have been the object of a great deal of investment. In the categories of conjugated polymers, polyfluorene (PF) and poly(phenylene-vinilene) (PPV) and their derivatives occupy a significant position. In the last years, polymers contended PF and PPV units were synthesized for application in emitting devices with different luminescence colors, inclining white light-emitting diodes (WLEDs). In particular, the PDHFPPV has been widely used in these devices, but your backbone presents vinylic bonds that is susceptible at photoxidation process, and this effect has not received attention. Understanding the PDHFPPV photoxidation and stability are important to increase the lifetime of your devices and to evaluate the possibility of applying this polymer in radiation sensors such as those already developed for the MEH-PPV. In the present work, we investigate the photo-oxidation process and your effects in the optical properties of PDHFPPV by using UV-VIS absorption, and photoluminescence spectroscopes. The changes in color of the radiation emitted by the polymer were also analyzed using the chromatic coordinate, the most practical color map for the lighting designer or technician. Finally, in order to evaluate the role of the radiation on the chemical structure of the polymer backbone, it was followed by gel permeation chromatography, as well as solid state NMR e IR spectroscopes and mass spectrometry. The results show inclusion of carbonyl within the polymeric chain, aldehydes formation and scission of polymer backbone with associated decreasing in the intensity of the absorption spectra. Because degradation is based on a photoreaction mechanism, the incorporation rate of carbonyl within the polymeric chain for the real polymer depends on its exposure time to blue-light radiation, which is very useful for the purposes of using the polymer as the basis for a dosimeter. Finally, we find that the absence of oxygen and the presence of radical scavengers can reduce the kinetic of materials degradation. This work was sponsored by Fapemig, Capes, CNPq and INEO/CNPq.
9:00 PM - HH3.30
White Light Emission from GaN-polymer Composites.
Basant Chitara 1 2 , C.n.r. Rao 2 1 , S.b Krupanidhi 1 2
1 Materials Research Centre, Indian Institute of Science, Bangalore, Karnataka, India, 2 CPMU, ICMS, Bangalore, Karnataka, India
Show AbstractAbstractRecently, tremendous progress has been achieved in GaN-based light-emitting diodes (LEDs). This has resulted in a variety of applications such as traffic light, full color display, optical storage, and lighting. For the case of lighting, white light can be generated by several different methods. The most commonly used method is to combine a phosphor wavelength converter with a GaN blue LED chip. The blue light emitted from the GaN LED is absorbed by the phosphor and re-emitted as long-wavelength phosphorescence. Thus, white light can be generated by the combination of the two emission bands.In order to fabricate Blue LED, One has to grow p- type GaN which is extremely difficult to grow. This prompted us to make white light from GaN where we have used p- type polymer as an alternate to p-type GaN to create p-n junction. The polymer used was F8BT Poly(9,9-dioctylfluorene-alt-benzothiadiazole) which is air stable and it can be spin coated over GaN. In addition to p type layer, this polymer will also emit yellow light which when combined with GaN blue emission will give rise to white light. Result to be discussed in detail.
9:00 PM - HH3.4
Electrical Characterization of Ultrathin PANI/PVS Films and Their Application to Ammonia Gas Sensor.
Mirela Santos 2 1 , Fabricio Santos 1 , Igor Marques 1 , Lucas Viana 1 , Gislayne Goncalves 1 3 , Rodrigo Bianchi 1
2 Physics Department, University Federal Of Viçosa, Viçosa, Minas Gerais, Brazil, 1 Department of Physics, Federal University of Ouro Preto, Ouro Preto, MG, Brazil, 3 , Federal Institute of Minas Gerais - Campus Ouro Preto, Ouro Preto, Minas Gerais, Brazil
Show AbstractGas sensors based on conducting polymers are particularly attractive as these materials can be modified chemically to exhibit a high sensitivity to a different acid and base gases, and have technological potential for environmental control. Among the most important conducting polymers, polyaniline (PANI) appears as a potential candidate for gas sensors due to its ability to behave either as insulator or semiconductor or as metal, depending on the degree and type of doping used. In special, ammonia gas (NH3) is one of the offensive odors to be eliminated from poultry house and the detection of such gas (0-50 ppm range) becomes extremely important for environmental protection and also for health of poultry farmers. Forthat reason, it is very useful to develop NH3 sensor of low-cost and high sensitivity. In this work we investigated the optical, electrical and morphological properties of ultrathin PANI/PVS films as active material of ammonia sensor in a poultry house application. Thelayer-by-layer polymer films were deposited onto NiCr interdigitated microelectrode recovered with Au (NiCr/Au) line arrays. The buildup of the multilayers was monitored at each deposition step by UV-VIS spectroscopy while the atomic force microscopy (AFM) was employed to monitor the change in the roughness, in the grain and particle sizes. Current vs. voltage (I vs. V) curves were obtained for layer-by-layer films in a low voltage regime (< 105V/m), while the complex impedance measurements were carried out in 1 – 106 Hz frequency range. The results for I vs. V measurements show a perfect ohmic behavior irrespectively of the polymer thickness, while the complex impedance measurements showed a typical behavior of solid disordered materials, where the real component exhibits a plateau at low frequencies decreasing for higher values of frequencies which defines the relaxation times (τ)of the material. When the sensor was exposed to NH3 (0-50 ppm) it was observed an increase of dc impedance of the films at about three orders of magnitude as well of τ value, although there is no change of macroscopic color and morphology of the material. As part of the sensordevelopment effort, design rules were applied to optimize the electrical sensibility to NH3, and fundamental parameter as ammonia concentration, temperature and humidity were determined via laboratory measurements. The new sensor design includes considerations ofhardware and software to enable fast data acquisition, resulting in a robust amperometric sensor that is promising for poultry house control applications.This work was sponsored by Fapemig, CAPES, INEO/CNPq and CNPq.
9:00 PM - HH3.5
Polymer Nanocomposites for Magnetic Actuation.
Mitra Yoonessi 1 2 , Ileana Carpen 3 , Francisco Sola 2 , Michael Meador 2
1 , Ohio Aerospace Institute, Cleveland, Ohio, United States, 2 , NASA Glenn Research Center, Cleveland, Ohio, United States, 3 , Tennessee Tech University, Cleveland, Tennessee, United States
Show AbstractSmart adaptive materials are an important class of materials which can be used in space deployable structures, morphing wings, and structural air vehicle components where remote actuation can improve fuel efficiency. Adaptive materials can undergo deformation when exposed to external stimuli such as electric fields, thermal gradients, radiation (IR, UV, etc.), chemical and electrochemical actuation, and magnetic field. Large strain, controlled and repetitive actuation are important characteristics of smart adaptive materials. Polymer nanocomposites can be tailored as shape memory polymers and actuators. Magnetic actuation of polymer nanocomposites using a range of iron, iron cobalt, and iron manganese nanoparticles is presented. The iron-based nanoparticles were synthesized using the soft template (1) and Sun’s (2) methods. The nanoparticles shape and size were examined using TEM. The crystalline structure and domain size were evaluated using WAXS. Surface modifications of the nanoparticles were performed to improve dispersion, and were characterized with IR and TGA. TPU nanocomposites exhibited actuation for ~2wt% nanoparticle loading in an applied magnetic field. Large deformation and fast recovery were observed. These nanocomposites represent a promising potential for new generation of smart materials.Ref: 1)Pal, S.K., Bahadur, D. Materials Letters, 2010, 64, 1127-1129.2)Sun, S., Zeng, H., Robinson, D.B., Raoux, S., Rice, P.M., Wang S.X., Li G. J. Am. Chem. Soc., 2004, 126, 273–279.
9:00 PM - HH3.6
Polymer-based Catch Bond.
Hsieh Chen 1 , Alfredo Alexander-Katz 1
1 Department of Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractCatch bonds was discovered experimentally at the beginning of this century. However, their origin is still controversial. Here we demonstrate that this interesting behavior can be achieved using self-interacting polymers. The idea of self-interacting domains comes from the study of the multimeric protein von Willebrand factor (vWF), which plays an essential role in the initial stage of blood clotting. The A1 domain of vWF contains the binding site for platelet glycoprotein GPIbα. However, it has been shown that the neighboring A2 domain interferes with the GPIbα-binding conformation in A1 domain, blocking GPIbα-mediated platelet adhesion.In this study we use coarse-grained simulations and a kinetic theory description to demonstrate that a multimeric protein, with self-interacting domain pairs, can display catch-bond behavior. In particular, we show that in the small force regime the two interacting domains along the protein are attached most of the time, masking the binding sites to the ligands. However, under an externally applied force the probability of detaching these domains increases, and in turn the probability to form longer lifetime ligand-receptor bonds also increases. In the large force regime, the mean lifetime is dominated by the force dependence of single ligand-receptor pairs since the two domains are detached most of the time and behave as independent bonding sites. Our results are in agreement with experimental results on the force-bond lifetimes, as well as in the force range for maximum bond lifetimes.
9:00 PM - HH3.7
Mechanical and Drug Release Properties of Anisometric Hydrogels Having Thermal Responsive Behavior.
Sona Lee 1 , Sunae Hwang 1 , Jonghwi Lee 1
1 Chemical Engineering and Materials Science , Chung-Ang University, Seoul Korea (the Republic of)
Show AbstractRecently anisometric hydrogels have been developed and investigated as novel materials for sensors, scaffolds, drug delivery carriers, etc. Can the symmetry in IPN hydrogels influence mechanical and swelling properties when their composition and crosslink density remain the same? To elucidate the influence of anisometric structure, isometric and anisometric IPN hydrogels of poly(N-isopropylacrylamide), which has a lower critical solution temperature at 37 degrees Celsius, and poly(acrylamide) (PAAm) were prepared using nanoclay crosslinkers. Anisometric hydrogels (AIPN) could easily be fractured due to the mismatch in modulus. After resolving the fracture problems by engineering modulus, the resulting hydrogels distinctly showed the effects of symmetry. Swelling ratio, fracture propagation and drug release tests at 37 degrees Celsius (cilostazol) were evaluated. Uniaxial compression tests revealed that the modulus of these hydrogels increased with the concentration of PAAm. Anisometric hydrogels showed a slower swelling rate and a lower equilibrium swelling ratio. The anisometric structures of AIPN could also determine thermal responsive rate. Overall, by controlling the morphology and structure of AIPN, a wide range of mechanical and swelling properties are available from novel applications.
9:00 PM - HH3.8
Material to Enable the Selective Pre-concentration and Analysis of Actinide Ions from Solution.
Dominic Peterson 1 , Edward Gonzales 1 , Crystal Tulley 1 , Claudine Armenta 1 , Jaclyn Herrera 1
1 Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractIn recent years, we have introduced a material that incorporates both a ligand that is selective for the extraction of radioactive analytes and a polymer backbone to provide rigidity. The extractive functionality of the material can be controlled by either the pH of the analyte solution, or by adding sodium nitrate to enhance selectivity. We will demonstrate this approach to selectively remove an analyte of interest from a mixed solution. Our primary application for this material is for the extraction of multi-valent actinide cations in solution. For instance, plutonium can be extracted from a solution that also contains americium and uranium. Changing the conditions enables the extraction of americium from the same solution, and still other conditions enable the extraction of the uranium. The simplicity of this material enables the rapid pre-concentration and separation of actinides, which otherwise would require extensive radiochemical separation. In addition to replacing traditional wet chemistry methods, this material pre-concentrates the analytes onto a flat surface, which enables the analyte to be directly analyzed utilizing alpha spectrometry. Normally, the radioactive actinide analyte would need to be prepared onto a surface utilizing electroplating. Parameters for creation of the material as well as the performance under different conditions will be discussed. (LAUR-10-4137)
9:00 PM - HH3.9
Hydrolyzed Polyacrylonitrile Particles for Intelligent Heat Generating Materials.
Young Ho Kim 1 2 , Won Seon Lee 1 2 , Hyeon Tae Cho 1 , Jeong Cheol Kim 3
1 Organic Materials and Fiber Eng., Soongsil University, Seoul Korea (the Republic of), 2 Intelligent Textile Research Center, Seoul National University, Seoul Korea (the Republic of), 3 Energy and Applied Optics Team, Korea Institute of Industrial Technology, Gwangju Korea (the Republic of)
Show AbstractCross-linked, highly hydrophilic polymers can be used as moisture absorption-heat generating materials since some heat is released due to the exothermic process of moisture absorption. In this study, various sizes of PAN nanoparticles were successively synthesized via a dispersion/emulsion polymerization of acrylonitrile, cross-linked with hydrazine, and hydrolyzed with alkali. The effects of hydrazine concentration and hydrolysis condition on the degree of hydrolysis, particle shape, and heat release property were investigated. High hydrophilicity and non-solubility in water were imparted to the particles by successive cross-linking and hydrolysis. The particles maintained their shape after hydrolysis when they were cross-linked with a hydrazine concentration of more than 3%. When 0.3g of the hydrolyzed PAN particle was put into 1 g of water the temperature increase was up to 12 °C, which is large enough for heat generating materials. The same method of cross-linking and hydrolysis can be applied to PAN fibers to be used as heat generating clothes.
Symposium Organizers
Zhongyang Cheng Auburn University
Vivek Bharti 3M Company
Zhuo Xu Xi’an Jiaotong University
Debra A. Wrobleski Los Alamos National Laboratory
HH6: Poster Session
Session Chairs
Tuesday PM, November 30, 2010
Exhibition Hall D (Hynes)
HH4: Conductive and Semiconductive Polymers
Session Chairs
Iain Anderson
Debra Wrobleski
Tuesday PM, November 30, 2010
Back Bay B (Sheraton)
9:30 AM - **HH4.1
Electrically Conducting Polymers for Capacitors.
Youlong Xu 1 , Jingping Wang 1 , Jie Wang 1
1 Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education, Xian Jiaotong University, Xian, Shaanxi Province, China
Show AbstractElectrically Conducting Polymers (ECP), such as polypyrrole (PPy), polyaniline (PANi) and poly (3, 4-ethylenedioxythiophene) (PEDOT) are very important functional materials. PPy and PEDOT is a friendly environment, good conductivity, excellent stability, and etc. They also play a key role in capacitors, such as solid electrolytic capacitor and supercapacitor. In solid electrolytic capacitor, PPy was used to as a cathode. Because electropolymerized PPy is of high electronic conductivity and excellent thermal stability, solid electrolytic capacitor with PPy cathode is a nearly ideal capacitor, which has milliohm level of equivalent series resistance at 100 kHz, nearly linear relationship of impedance with frequency. In supercapacitor, porous PPy film, PPy/ PEDOT composite and F-SWNT/PPy composite were carried out for active electrodes. When pulsed electropolymerization, the electrodes can exceed to the specific capacitance of 200F/g and have the cycleability more than 100 thousands.
10:00 AM - HH4.2
Ion Transport and Storage in Ionic Polymer Bending Actuators.
Junhong Lin 1 , Yang Liu 2 , Gokhan Hatipoglu 2 , Qiming Zhang 2 1
1 Materials Science and Engineering Department, The Pennsylvania State University, State college, Pennsylvania, United States, 2 Electrical Engineering Department, The Pennsylvania State University, State College, Pennsylvania, United States
Show AbstractThe actuation of ionic polymer actuators is mainly caused by the charge transport and excess ion storage in the membrane and composite electrodes. The transient response of the ionic polymer membranes and composites in response to a step voltage can provide insights on the charge transport, storage, and distribution behaviors in the membranes and composites. This study investigates the charge transport behavior in pure ionic liquid and in ionomer membranes composites with different ionic liquids. The results show that the charges not only interact with the applied field but also interact with the membrane matrix and composites leading to a mobility drop when comparing to that in the pure ionic liquids. Therefore, in these membrane matrix and composites, the charge mobility is not only field dependent but also IL uptake dependent. It was found that the bending actuation in pure ionic polymer membranes was a result of micrometer thick charge layers accumulated on the electrodes. Also, a critical uptake and a field dependent effect of charge transport behavior were observed.
10:15 AM - HH4.3
Synthesis of Conducting Functional Copolymer by Oxidative Chemical Vapor Deposition (oCVD) and Its Sensor Application.
Dhiman Bhattacharyya 1 , Karen Gleason 1
1 Chemical Engineering Department, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractPolymeric electronic materials are gaining interests in the areas of fabricating flexible OLED, sensors, photovoltaic devices. There are various techniques to synthesize and fabricate these materials for device applications, including spin coating and solution processing. However, most of the currently applied methods involve multi-step synthesis and large quantities of solvents for fabrication. In this work, we present a single step and solvent free preparation of thin conducting copolymeric films by oxidative chemical vapor deposition (oCVD) process. This low temperature oCVD process shows promises for coating any substrate, for example, paper, plastics, silicon and glass with highly conducting, conformal polymeric films. Here, 3,4-ethylenedioxythiophene (EDOT) and 3-thiopheneethanol (3-TE) were employed to synthesize conducting copolymeric (poly-(EDOT-co-3-TE)) films. The available –OH functional groups in the copolymers were used for further derivatization reactions. The copolymeric films were characterized by FT-IR, UV-Vis and X-ray photoelectron spectroscopies and 4-point probe measurements. In addition to that, detection of specific biomolecules at a lower response time and selectivity has been demonstrated.
10:30 AM - HH4.4
Understanding Ionic Actuators.
Ralph Colby 1 2 , Reuben Bushnell 1 2 , Qiming Zhang 3 2
1 Materials Science and Engineering, Penn State University, University Park, Pennsylvania, United States, 2 Materials Research Institute, Penn State University, University Park, Pennsylvania, United States, 3 Electrical Engineering, Penn State University, University Park, Pennsylvania, United States
Show AbstractPolarization of ions at electrodes can be exploited to make devices that convert electrical energy to mechanical energy [1]. We explore the effects of electrode surface area and applied voltage on the charge polarization, using a.c. and d.c. dielectric methods. At low applied voltages, the 1953 Macdonald model [2] (a mean-field solution to the Poisson-Boltzmann equation) describes the monotonic decay of the concentrations of ions polarizing near each electrode. At higher voltages (still below any electrochemical limit) the 2007 Kornyshev model [3] is used to understand the multi-layer structure of positive and negative ions near each electrode and why the efficiency of ionic actuators plummets as voltage is increased. [1] J. D. W. Madden, et al., IEEE J. Oceanic Eng. 29, 706 (2004). [2] J. R. Macdonald, Phys. Rev. 92, 4 (1953). [3] A. A. Kornyshev, J. Phys. Chem. B 111, 5545 (2007).
10:45 AM - HH4.5
Fiber Field-effect Device via In-situ As-Se-Te Channel Crystallization.
Sylvain Danto 1 , Fabien Sorin 1 , Nicholas Orf 1 , Zheng Wang 1 , John Joannopoulos 1 , Yoel Fink 1
1 , MIT, Cambridge, Massachusetts, United States
Show AbstractGlassy chalcogenide compounds have been shown to co-draw with metals and polymeric insulators into tens-of-meters-long, light-weight and flexible fibers with unusual functionalities. To date, however, these multimaterial fibers exhibit limited electrical performance due to the use of thermally stable glasses. Here we demonstrate that the competing requirements for thermal drawing and subsequent phase-change in amorphous semiconductors can be reconciled to incorporate crystalline semiconductors into multimaterial fibers. To demonstrate the in-situ crystallization scheme, we fabricate a fiber constituted of a solid-core As-Se-Te glass in contact with four Sn electrodes and surrounded with a polymeric PES cladding. Subsequently fiber pieces of similar geometry are isothermally annealed. XRD and DSC investigations reveal the growth with annealing time of a crystalline phase within the glassy matrix. The phase-change of the semiconductor, which leads to a large decrease in defect density, results in a concomitant five-order-of-magnitude decrease in resistivity of the metal-insulator-crystalline semiconductor structure. Using this technique, we present the first fully integrated p-channel field-effect fiber device with gate-voltage-controlled conduction between source and drain electrodes. The fiber consists of two identical field-effect devices, each one of them being made of two parallel source and drain Sn electrodes contacted by a semiconducting p-type As-Se-Te film. A third Sn electrode is used as the gate, separated from the channel by an insulating PES polymer film. We show a clear modulation of the source-to-drain current IDS, revealing an unpinned Fermi level, and a substantial improvement of the mobility of the crystalline semiconductor over the amorphous state.Here we demonstrate the integration of a phase-changing glassy semiconductor compatible with thermal drawing inside a fiber and we present a fiber field-effect device fabricated via the in-situ crystallization of the channel. This result will serve as a building block for large-scale fiber-integrated digital circuits, paving the way towards optoelectronic and logic operations in polymer fibers and fabrics.
11:30 AM - HH4.6
Photoconductive Gain in Aligned PBTTT Nanoribbons Based Planar Photodiodes.
Dhritiman Gupta 1 , Sebastian Albert-Seifried 1 , Martin Heeney 2 , Iain McCulloch 3 , Henning Sirringhaus 1
1 Physics, University of Cambridge, Cambridge United Kingdom, 2 , University of London, London, E1 4NS United Kingdom, 3 , Imperial College of London, London, SW7 2AZ United Kingdom
Show AbstractIn polymer photodiodes largely based on donor-acceptor blends, charge separation and transport largely depends on blend morphology and crystalline packing of the polymer chains. However recently it has been reported that the non-geminate charge carrier recombination might get affected by the preferential alignment of polymer chains along the field direction [1], [2]. It is interesting to study the effect of chain alignment along the field on the geminate-pair recombination as well. Semicrystalline polymer like alkyl substituted polythiophene, poly (2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophene) (PBTTT) is a potential candidate for photovoltaic application due its high charge carrier mobility, low photoluminescence efficiency and better stability due to deep HOMO level [3]. It has been recently reported that PBTTT forms a distinct nanoribbon phase when annealed over 290 C. Several microns long nanometer wide ribbons are formed by the edge-on π-π stacking of the fully chain-extended PBTTT backbones along the length of the nanoribbons [4]. Nanoribbons can be aligned over several microns using Zone-Casting method which shows high optical anisotropy. In this study we fabricated planar diodes based on aligned PBTTT nanoribbons and characterized the charge generation/transport anisotropy by measuring external quantum efficiency (EQE) under illumination. By illuminating the device with a pulse of light we reveal a slow decay of photocurrent over several hours indicating trapping of charge carriers. Trapped charge carriers give rise to photoconductive gain which is reflected in measured EQE as high as 10^5% under constant illumination. However in order to find out the EQE due to genuine photogeneration, measurement under pulsed illumination was carried out with a constant bias light illumination. Photocurrent transients, recorded for a small intensity pulse along with the constant bias light, show more linear behaviour of photocurrent with intensity indicating some genuine photogeneration. We will discuss about the possibility of revealing the anisotropy in efficiency of exciton dissociation and genuine photogeneration of charges.[1] J. Zaumseil, et. al., Adv. Funct. Mater., 18, 3630–3637 (2008).[2] C. Groves, et.al., Phys Rev. B., 78, 155205 (2008).[3] I. Mcculloch, et.al. Nature Mater. 5, 328 (2006).[4] D. M. Delongchamp, et. al. ACS Nano, 3, 780 (2009).
11:45 AM - HH4.7
Investigation of Inherently Conductive Polymer as Structure Health Monitoring Sensor for Composite.
Huaxiang Yang 1 , Dongsik Kim 1 , Abhishek Singh 1 , Brady Pitts 1 , Gregory Tregre 1 , Patrick Kinlen 2
1 , Crosslink, Hattiesburg, Mississippi, United States, 2 , Crosslink, St. Louis, Missouri, United States
Show AbstractA soluble polyaniline was synthesized through emulsion polymerization and characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), gel permeation chromatography (GPC), viscosity as well as coefficient of linear thermal expansion (CLTE). The electrical conductivity could reach 1000 S//cm with a certain post treatment. Its multiple printabilities (draw down, spray, inkjet print, screen print as well as aerosol jet print) make it feasible for various patterns of sensors. The electormechanical response of these sensors was used to sense strain/stress or damage of composite under load condition, which imitates aircraft operation condition. This kind of sensor provides a feasible real time monitoring system for composites with adding almost “zero” weight onto substrate.
12:00 PM - HH4.8
Conductive Polymer Bilayers – A Spectroelectrochemical Look at Their Doping Reactions.
Henrik Gustafsson 1 , Carita Kvarnstrom 2 , Ari Ivaska 1
1 Process Chemistry Centre/Laboratory of Analytical Chemistry, Åbo Akademi University, Åbo - Turku Finland, 2 Turku University Centre for Materials and Surfaces/Laboratory for Materials Chemistry and Chemical Analysis/Department of Chemistry, University of Turku, Turku Finland
Show AbstractPoly(benzobisimidazobenzophenanthroline), BBL, is an n-dopable ladder polymer. Few applications have been found for pristine BBL, since the unmodified polymer has low solubility even in strong acidic solutions. Derivatization of the BBL end chains with poly(ethylene oxide), PEO, gives a water dispersible polymer more easy to process.Poly(3,4-ethylenedioxythiophene), PEDOT, is one of the few conducting polymers that are both p- and n-dopable. We have previously [1, 2] studied the doping behavior of electrochemically polymerized PEDOT doped with hexafluorophosphate, PEDOT(PF6), on aluminum.In this work, we study bilayers of electropolymerized PEDOT(PF6) and drop-cast BBL-PEO. In such a system, PEDOT acts as electron donor while BBL acts as acceptor. From an application point of view, a BBL–PEDOT bilayer might be of interest as charge transport material in, for instance, organic or hybrid solar cells.The doping behavior of the bilayer structures was studied with cyclic voltammetry, and with in situ ultraviolet-visible and attenuated total reflectance Fourier transform infrared spectroscopy. The discharging behavior of both single layers of PEDOT(PF6) and BBL-PEO and for bilayers was studied with chronopotentiometry.The spectroelectrochemical characterization of the bilayers provided us with fundamental information about the properties of the materials, giving insight in the structural and electronic changes taking place in the polymer films during doping and subsequent dedoping. This information is essential in order to be able to use the conducting polymers in future real-life applications, e.g., as organic semiconducting components.References:[1] H. Gustafsson, C. Kvarnström, A. Ivaska, Thin Solid Films 517 (2008) 474[2] F. Sundfors, H. Gustafsson, A. Ivaska, C. Kvarnström, J Solid State Electrochem 14 (2010) 1185
12:15 PM - HH4.9
Poly (aniline- m-aminobenzoic acid)- Poly (vinyl alcohol) Composite: Synthesis and Ester Sensing.
Sarbani Adhikari 1 , Pallab Banerji 1
1 Materials Science Centre, Indian Institute of Technology, Kharagpur, Kharagpur India
Show AbstractPlants respond to herbivore damage with the release of volatile organic compounds (VOCs). VOCs released from plants consist mainly of products of the shikimic acid-pathway, fatty acid-derived products and terpenes, isomeric hexenyl butyrates, 2- methyl butyrates, indole and Z-3- hexenyl acetate. Sensing of these VOCs released from plants can be used as a measure to control damage caused to plants due to pest attack. Here we report the synthesis of poly (aniline-co- m-aminobenzoic acid) on maleic acid (MA) cross-linked Poly (vinyl alcohol) (PVA) by oxidative polymerization of aniline hydrochloride (AnHCl) and m-aminobenzoic acid (m-ABA) using ammonium persulfate (APS) as oxidant for ester (hexenyl butyrate) sensing. Instead of conventional solution polymerization, here synthesis is carried out on APS soaked MA crosslinked PVA (MA-PVA) film where the polymer in its conducting form is in situ deposited on the MA-PVA membrane. The composite of the copolymer with PVA is obtained in the conducting form as a film which does not require further processing. The composite film was characterized by FTIR and UV-VIS spectroscopy, and electrical measurements. The composite of poly (aniline-co-m-aminobenzoic acid) with PVA was prepared by keeping the APS/AnHCl ratio 0.233. The ratio of AnHCl/mABA was 2. MA-PVA film was first kept immersed in water for 24 h to remove uncross-linked PVA and MA. The film was then dried by keeping in a covered glass chamber at ambient temperature for 24 h. A saturated solution of APS was separately prepared by dissolving 8 g APS in 10 ml water. Next the dry MA-PVA film was immersed in APS solution for a maximum time of 6 h during which the films swelled. The swollen film started darkening immediately after immersion due to formation of the copolymer. The film was kept in the monomer solution for overnight to ensure complete polymerization in the MA-PVA matrix. The film was dried by keeping in a covered glass chamber at ambient temperature for 24 h and then heated in a vacuum oven at 60 °C for 2 h. The real-time resistance changes of the composite films monitored with a source meter upon exposure to 53 ppm and 66 ppm of hexenyl acetate. Air was used as the carrier gas. The resistance of the sensor was recorded continuously during three successive cycles of analyte exposure. The resistance of the copolymer increases upon exposure to the ester. The resistance then decreases as the ester flow is stopped. The ester sensing here is a reversible process. Esters are hydrolyzed by both acids and bases. The carbonyl oxygen of the ester abstracts a proton from the carboxylic acid group attached with the polyaniline chain. Abstraction of a proton from the carboxylic acid group affects the conjugation along the polyaniline chain and its conductivity changes. But the hydrolysis reaction does not proceed to completion due to the absence of water molecule. Hence the polymer is reverted to its initial stage as the ester flow is stopped.
12:30 PM - HH4.10
Performance and Stability Improvement of P3HT:PCBM Based Solar Cells by Chromium Oxide Interfacial Layer.
Mingdong Wang 1 , Qin Tang 2 , Jin An 1 , Jianbin Xu 1
1 Electronic Engineering, The Chinese University of Hong Kong, Hong Kong China, 2 Chemistry, The Chinese university of Hong Kong, Hong Kong Hong Kong
Show AbstractWe report on the chromium oxide as cathode interfacial layer to improve the efficiency and stability in air for the bulk heterojunction solar cells of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM). Devices with chromium oxide interfacial layers show higher power conversion efficiency (PCE) and stability than those without interfacial layer or with conventional one (e.g. LiF). Devices with chromium oxide interfacial layer improved the stability over 100 times than devices without interfacial layer or LiF interfacial layer in air without any extra package.
12:45 PM - HH4.11
Fabrication of a Planer-type Ionic Polymer Actuator Fabricated with MEMS Technology.
Kunitomo Kikuchi 1 , Shigeki Tsuchitani 1 , Ippei Shimizu 2
1 Department of Opto-Mechatronics, Faculty of Systems Engineering, Wakayama University, Wakayama Japan, 2 Graduate School of Systems Engineering, Wakayama University, Wakayama Japan
Show AbstractIonic polymer-metal composite (IPMC) is one of the most attractive materials for soft actuators because it exhibits large strain under low application voltages lower than 2 or 3 V.It consists of a polyelectrolyte membrane and thin noble metal electrodes formed on the both surfaces of the membrane. In conventional IPMCs, commercialized polyelectrolyte membranes were mainly used. So, it is difficult to fabricated miniaturized IPMC freely, because it is generally used by cutting into small pieces.By combining IPMC fabrication technologies with micro machining technologies, we can make miniaturized IPMCs having large strain together with micro electro-mechanical systems (MEMS) devices.There are many technological subjects to fabricate miniaturized IPMCs using micro machining technologies. One is fabrication of micro structures of polyelectrolyte membrane on substrates without peeling, since polyelectrolyte membranes expand very much by absorbing water. For example, the linier expansion ratio is 10% when Nafion® membranes (DuPont) are used. We developed a fabrication technique of micro structures of polyelectrolyte membranes on the substrates without peeling using casting method with polyelectrolyte dispersion solution. In this method, the adhesion force of the membranes with silicon substrate was remarkably improved by roughening the substrate by anodic oxidation of silicon. Small patterns of the polyelectrolyte membranes on the substrate were formed by a photo lithography technique using O2 plasma etching.The second technological subject is formation method of the electrodes on the both sides of the polyelectrolyte membrane, which are adhered on the substrate. Conventionally, the most reliable formation method of the electrodes of IPMC is a chemical plating method. We already developed a formation technique of patterned electrodes on commercialized polyelectrolyte membranes using photolithography techniques. The patterned electrodes were fabricated with the chemical plating method by covering polyelectrolytes with photo resist patterns.In the presentation, we will describe the fabrication of the planer-type IPMC formed on the silicon substrate by combining the developed micro fabrication techniques of the IPMC described above.
HH5: Optical / Mechanical Properties and Devices
Session Chairs
Vivek Bharti
Stephen Ducharme
Tuesday PM, November 30, 2010
Back Bay B (Sheraton)
2:30 PM - HH5.1
Reversible and Reprogrammable Color Switching in Two-dimensional Photonic Structures Triggered by Shape Memory Effect.
Jie Li 1 , Xuelian Zhu 1 , Shu Yang 1
1 Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractPeriodic structures have been widely used as photonic and phononic crystals. It will be attractive to reversibly tune the photonic and phononic properties simply by changing the pattern shape triggered by an external stimulus. In addition, it will be highly desirable to reprogram such shape change from the same material on-demand when applying different stimuli. In this study, we demonstrate reversible color change, analogous to photochromic transition, triggered by shape memory effect in a 2D membrane with a periodic array of micronscaled holes. The shape memory polymer (SMP) membranes were fabricated by imprint lithography from a mixture of diglycidyl ether of bisphenol A epoxy (EPON 826), poly(propylene glycol)bis(2-aminopropyl)ether and decylamine. The transition temperature of the SMP can be tuned from 40OC to 90OC by varying the ratio of two amines. The as-fabricated 2D periodic structure has an intrinsic structural color due to Bragg diffraction. After being compressed under a hot press above the transition temperature, the 2D structure was deformed, leading to pattern transformation, e.g. from a p6mm hexagonal lattice of circular holes to a new pattern with elliptical shaped holes having a p2gg symmetry with glide symmetries. When the pores were nearly closed, the film became highly transparent; the degree of deformation, thus color change, can be modulated by the load when heated. Because of the shape memory effect, the deformed pattern can be completely recovered upon reheating, allowing for reversible and reprogrammable color change. The combination of pattern transformation and shape memory effect will advance applications, including sensors, optical switches, and data storage devices.
2:45 PM - HH5.2
Highly Temperature- and UV-Resistant Polybenzoxazines Prepared From Siloxane-Imide–containing Benzoxazines.
KaiChi Chen 1 2 , HsunTien Li 1 , ShuChen Huang 1 , WenBin Chen 1
1 Material and Chemical Research Laboratories, Industrial Technology Research Institute, Hsinchu Taiwan, 2 Institute of Applied Chemistry, INational Chiao-Tung University, Hsinchu Taiwan
Show AbstractA liquid siloxane-imide-containing benzoxazine, BZ-A6, has been successfully synthesized. The thermal properties of the polybenzoxazine prepared from BZ-A6 (PBZ-A6) are superior to those of conventional PBZs lacking siloxane groups. PBZ-A6 exhibited a high decomposition temperature (463.7 °C) and a high residual weight (50.9 wt%); its glass transition temperature was 186.4 °C. Toughening of brittle PBZs can be achieved by adding siloxane-imide segments; indeed, PBZ-A6 provided free-standing, bendable films. PBZ-A6 possessed an extremely low surface free energy (γs = 12.4 mJ/m2) after curing at 230 °C for 1 hr. Moreover, the surface free energy of PBZ-A6 was less than that of PBa, a conventional bisphenol-A–type PBZ, after thermal treatment (230 °C for 24 hrs) or UV exposure (UV-A for 500 hrs), suggesting that siloxane-imide PBZs are more suitable for application as low-surface-free-energy materials that are highly temperature- and/or UV-resistant. PBZ-A6 might also be useful in weather-resistant materials because of its low surface free energy and its good thermal and UV resistance.
3:00 PM - HH5.3
Kilometer-long, Highly Ordered Uniform Piezoelectric Nanotubes.
Mehmet Kanik 1 , Mecit Yaman 1 , Mehmet Bayindir 1 2
1 UNAM-Institute of Materials Science and Nanotechnology, Bilkent University, Ankara Turkey, 2 Department of Physics, Bilkent University, Ankara Turkey
Show AbstractThere has been a recent surge in the interest for piezoelectric stimuli responsive materials due to their many potential application areas such as sensing and actuation, energy scavenging, MEMs devices and in artificial muscle and skin design.There is still an ongoing research to produce flexible, ordered and high efficiency piezoelectric materials to be used in some of these applications. We have recently introduced a new top-down method to fabricate extremely long ordered poly(vinylidene floride) (PVDF) nanotubes with extended lengths and very high aspect ratios. In this context PVDF is a new piezoelectric material with fascinating properties such as high flexibility and low density compared to the traditional piezoelectric materials.Conventional nanotubes are generally synthesized by bottom up techniques often resulting in inhomogeneous, disordered nanostructures. Here we report a novel top-down fiber drawing method to fabricate PVDF nanotubes with diameters less than 30 nm. The fabrication process comprises of three iterative fiber drawing steps; starting with a polysulphone (PSU) rod, with a hollow core, that is filled with rolled PVDF sheets. First fiber drawing step successfully produces PVDF microtubes with PSU cladding. Tube formation from the PVDF melt is due to high surface energy of these films. Fiber drawing process was iteratively repeated two more times to reduce the PVDF microtubes down to nanotubes. In this way, we have successfully fabricated highly ordered, kilometer-long piezoelectric PVDF nanotubes. Furthermore, it is possible to extract free standing PVDF nanotube structures by dissolving the PSU cladding using organics etchants. Smallest diameter of nanotubes that we attained is 25 nm which we believe can even be reduced down to a fraction of this value. Ordered kilometer long piezoelectric PVDF nanotubes are expected to bring unparalled opportunities for the artificial muscle and skin research.
3:15 PM - HH5.4
Three-dimensional Microvascular Fiber-reinforced Composites.
Aaron Esser-Kahn 1 2 , Piyush Thakre 5 2 , Jason Patrick 4 2 , Hefei Dong 3 2 , Nancy Sottos 3 2 , Scott White 5 2 , Jeffrey Moore 1 2
1 Chemistry, University of Illinois Urbana-Champaign, Urbana, Illinois, United States, 2 Beckman Institute, University of Illinois Urbana Champaign, 61801, Illinois, United States, 5 Aerospace Engineering, University of Illinois Urbana Champaign, Urbana, Illinois, United States, 4 Department of Civil and Environmental Engineering, University of Illinois Urbana Champaign, Urbana, Illinois, United States, 3 Materials Science and Engineering, University of Illinois Urbana Champaign, Urbana, Illinois, United States
Show AbstractMicrovascular systems are essential to a broad range of technological applications, including biotechnology, microelectronics, sensors, chemical reactors, and autonomic materials. Several approaches have emerged for fabricating three-dimensional (3D) microvascular systems including lithographic techniques, laser micromachining1, and various two-dimensional methods extended to 3D.. We have previously reported a method for the fabrication of 3D microvascular networks utilizing fugitive inks that allowed the creation of interconnected micro channels4 and demonstrated their use in the construction of self-healing coatings and materials5,6. Recently, sacrificial sugar fibers and hollow glass fibers have been used to create 3D microvascular networks2,3All of these methods have distinct advantages, but all still lack the ability to be integrated into large-scale fiber composite materials. Here we show a method for the creation of woven composite materials containing microvascular networks via interweaving of a sacrificial fiber. The polymeric fiber is sacrificed by heating the post-cure composite above the cure temperature, catalyzing depolymerization of the fiber into a gaseous monomer. These fibers are woven directly into glass and carbon fiber composites and after evacuation leave behind networks of interconnected empty channels that can be filled with fluid. This is an increase in both the size and complexity of previous microvascular systems while maintaining the critical ability to pattern networks. Composites formed with sacrificial fibers should facilitate thermal management in composites; enable more sophisticated self-healing materials and provide a test-bed for new self-healing chemistries.
3:30 PM - HH5.5
Flexible Optical Grating for Large Strain Sensing with High Sensitivity.
Hanqing Jiang 1 , Cunjiang Yu 1 , Teng Ma 1 , Hongbin Yu 1
1 , Arizona State University, Tempe, Arizona, United States
Show AbstractStrain measurement is important in a vast variety of applications for damage detection of mechanical and civil structures. Traditional metal strain gauges are limited in measuring large strain since they typically only measure strain up to around several percent. For example, platinum/tungsten (8%/92%) has the strain range of about ±0.3%. Strain sensors made of commercial fabrics coated with conductive polymers are able to detect a large strain deformation; however, the repeatability and reliability is limited. After frequent usage, the performance of this strain sensor reduces gradually due to the poor mechanical properties of the polymer, aging of polymer and reduction of adhesion, especially in cyclic deformation.Here we report an easily fabricated optical grating based strain sensor which is featured with large strain over 30%, and high sensitivity. The fabrication of the gratings involves depositing ultra-thin film onto pre-stretched elastomeric substrates. Specifically, a 1 mm thick polydimethylsiloxane (PDMS) is tensioned by a custom made stage at desired level, named pre-strain. An ultra-thin Pd/Au film about 8 nm thick is then deposited onto the tensioned substrate at room temperature. Releasing the pre-strain slowly after deposition leads a sinuous buckled profile with periodic wavelength around 800 nm: the top PDMS layer fluctuating with the Pd/Au film due to competition between each other. As mechanical strain is applied on the grating, the grating period changes, which can be reflected by the optical properties of the grating with high sensitivity. Specifically, the position of the diffraction light from monochromatic light incident onto the grating is measured. Any change of the diffraction light due to the grating period alternation is caused by mechanical strain. The grating can be stretched or compressed by large level of strains, which naturally suitable for large strain sensing. Strain within large range (20%) yet high resolution of 0.03% have been achieved.
3:45 PM - HH5.6
Lower Critical Solution Temperature (LCST) Polymers as a Self Adaptive Alternative to Mechanical Tracking for Solar Energy Harvesting Devices.
Philipp Schmaelzle 1 , Gregory Whiting 1
1 , Palo Alto Research Center (PARC), Palo Alto, California, United States
Show AbstractSolar energy harvesting devices (SEHD) often require tracking (mechanical movement) to follow the incident sunlight's changing angle through the day and year. This is done when concentrated radiant flux needs to be maintained on a receiver or coupling element in a photovoltaic system, or when the direct sunlight component needs to be handled selectively in a architectural daylighting system. However, the moving parts commonly used for this purpose are undesirable due to the mechanical complexity and cost they add. As an alternative to mechanical tracking, we employ a polymer solution displaying a lower critical solution temperature (LCST) which transitions by illumination (via heat) between two optically distinct states. Thereby, it can be employed as an optical coupler, which adaptively adjusts to the incoming sunlight (focused by a static lens array) and couples light into a lightguide. PV cells attached to the lightguide tap out concentrated light and convert it to electricity. Previous approaches have successfully demonstrated such passive lightguide based solar energy harvesting devices (PLG-SEHD), but had to resort to 2-axis tracking. To our knowledge, the work presented here is the first mechanically static variant of this promising class of devices. By circumventing the mechanical tracking requirement, we open the path to integrate PLG-SEHDs with glazing systems of built structures. In these applications, both photovoltaic electricity and tint-free daylight with reduced fluctuation is obtained from the system. Here, we will describe the system design of our untracked PLG-SEHD together with raytracing simulations and briefly review material properties relevant for this use of LCST polymers. A case study for a hybrid daylighting/photovoltaic application of our system is given together with performance estimates based on simulations with solar resource data from NREL. We conclude by experimentally demonstrating feasibility of this approach.
4:30 PM - HH5.7
Core-shell Microcapsules for the Visual Indication of Mechanical Damage.
Susan Odom 1 2 , Jericho Moll 1 3 , Aaron Finke 2 , Mary Caruso 1 2 , Alex Prokup 1 2 , Eric Elleby 2 , Nancy Sottos 1 3 , Scott White 1 4 , Jeffrey Moore 1 2
1 Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 Materials Science & Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 4 Aerospace Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractVisual indication of mechanical damage is important in identifying damaged / stressed areas in polymers and composites used as structurally supportive materials. Identifying damage can provide alert mechanisms to investigate the integrity of polymeric materials before catastrophic and/or irreversible system failure occurs. Herein we report the use of core-shell microcapsules in for the visual detection of mechanical damage. We present two mechanisms by which damage indication may be accomplished for using microcapsule systems to effect color change. In one case, colored charge transfer salts or conjugated chromophores are produced when two complementary microcapsules, consisting of solutions of separately encapsulated donors and acceptor components are combined. In a second mechanism, a polymerizable cyclooctatetraene core becomes colored after microcapsule release, upon which the core reacts with the Grubbs’-Love ruthenium catalyst, forming polyacetylene in a ring-opening metathesis polymerization reaction. Results from self-healing studies using the cyclooctatetraene-Grubbs’ system will also be presented.
4:45 PM - HH5.8
Motion of Elastic Microcapsules on Compliant Substrates Coated with Adhesive Ligands.
Egor Maresov 1 , German Kolmakov 1 , Anna Balazs 1
1 Chemical Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Show AbstractBy integrating mesoscale models for hydrodynamics, micromechanics and adhesion, we examine the fluid driven motion of elastic microcapsules on compliant surfaces. The capsules, modeled as three-dimensional fluid-filled elastic shell, represent polymeric microcapsules or biological cells (e.g., leukocytes). Our integrated Lattice Boltzmann model/Lattice spring model (LBM/LSM) approach allows for a dynamic interaction between the elastic capsule’s wall and surrounding fluid. To capture the interaction between the shell and the surface, we adopt the Bell model, which has been used to model the interaction of biological cell rolling on surfaces under the influence of an imposed shear. The exterior of the microcapsule is functionalized with receptors, whereas the substrate surface is coated with adhesive ligands. We tailor the values of the dissociation and association rate for the bonds between the shell and the surface to match the properties of the experimental systems. We examine how the capsule’s shell and substrate compliance and adhesive and mechanical patterning of the surface affect the capsule movement. The findings provide guidelines for creating smart surfaces that could regulate the microcapsule’s motion.
5:00 PM - HH5.9
Characterization of Mechanochemically Active Linear Polymers.
Sharlotte Kramer 1 2 , Brett Beiermann 1 2 , Douglas Davis 3 2 , Nancy Sottos 1 2 , Scott White 4 2 , Jeffrey Moore 3 2
1 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 4 Aerospace Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractBiological systems convert mechanical stimuli to other forms of energy such as electrical, thermal, or chemical. Force-sensitive molecules, called mechanophores, exhibit a chemical response to mechanical force and can be incorporated into the polymer chains. These polymers have potential to exhibit advantageous chemical responses activated by global mechanical force. We have previously demonstrated activation of a mechanophore called spiropyran, which undergoes a force-induced, 6-π electrocyclic ring-opening reaction accompanied by a color change, in linear polymers via sonication in solution and in bulk solids via tension and compression (Davis, et al., Nature 459: 68-71, 2009). Understanding the mechanism for transfer of macroscopic stress on a bulk solid polymer to the mechanophore remains a topic of active research. The proposed premise for mechanical activation in linear polymers is that linearly oriented polymer chains transfer force to the mechanophore more efficiently than a randomly oriented chain that will first use the mechanical energy to entropically deform. We have performed uniaxial tension experiments on two bulk linear solid spiropyran-linked polymers, elastomeric poly(methyl acrylate) (PMA) and glassy poly(methyl methacrylate) (PMMA) to highly align the polymer chains and activate the mechanophores. Since spiropyran-linked polymers not only change color, but also fluoresce, when the spiropyran activates, we simultaneously measured mechanophore fluorescence and the optical birefringence, which is related to chain orientation, via photoelasticity for the same field of view during tensile testing. These experiments elucidate the critical molecular orientation and macroscopic stress level required to activate the mechanophores, and provide data to guide the design of systems incorporating mechanochemically active polymers.
5:15 PM - HH5.10
Using Indentation to Characterize the Poroelasticity of Gels.
Yuhang Hu 1 , Xuanhe Zhao 1 , Joost Vlassak 1 , Zhigang Suo 1
1 , Harvard University, Cambridge, Massachusetts, United States
Show AbstractWhen an indenter is pressed into a gel to a fixed depth, the solvent in the gel migrates, and the force on the indenter relaxes. Within the theory of poroelasticity, the force relaxation curves for indenters of several types are obtained in a simple form, enabling indentation to be used with ease as a method for determining the elastic constants and permeability of the gel. The method is demonstrated with a conical indenter on an alginate hydrogel and on polydimethylsiloxane submerged in organic solvents.
5:30 PM - HH5.11
Mechanical Response of Intelligent Polymer Brushes at the Nanoscale.
Peter Schoen 1 , Fons Schreurs 1 , Xiafeng Sui 1 , G. Julius Vancso 1
1 Materials Science and Technology of Polymers, MESA+ Institute for Nanotechnology , University of Twente, Enschede Netherlands
Show AbstractFunctionalized polymer brushes have been used with great success to prepare designer surfaces that exhibit e.g. stimulus responsive (switchable) behavior that can be used as platforms in sensing and device applications, exhibit tunable adhesion, friction and protein adsorbing ability, etc. The grafting density can for example be controlled by using surface immobilized initiators with variable coverage by so-called “grafting from” approaches. Due to the very small thickness of the polymer films (typically between 10-200 nm) their quantitative characterization has been a difficult task. In this work, Atomic Force Microscopy (AFM) in combination with colloidal probing has been applied to monitor the mechanical properties of surface grafted polymer brushes. Poly(methacrylic acid) (PMAA) brushes have been used as model system. PMAA brushes were grafted from initiator-functionalized substrates by surface-initiated atom transfer radical polymerization of sodium methacrylate. Surface grafted brush layers were characterized by static contact angle measurements, grazing incidence fourier transform infrared spectroscopy and ellipsometry to determine the dry thickness of the brushes. Mechanical properties of the PMAA brushes have been investigated as function of layer thickness, brush density and solution pH value. The results provide new insight into the mechanical performance such as compressibility in comparison to existing AFM studies.References(1)Sui, X.; Zapotoczny, S.; Benetti, E.M. ; Schön, P. ; Vancso, G.J. Characterization and molecular engineering of surface-grafted polymer brushes across the length scales by atomic force microscopy. J. Mater. Chem., 2010, DOI: 10.1039/b924392e(2)E. M. Benetti. Molecular engineering of designer surfaces by controlled radical polymerizations: brushes, hedges and hybrid grafts. PhD thesis, University of Twente, 2009(3)A. Halperin, A. and Zhulina, E.B. . Atomic Force Microscopy of Polymer Brushes: Colloidal versus Sharp Tips. Langmuir 2010, 26(11), 8933–8940
5:45 PM - HH5.12
Microthermogravimetric Analysis of a Single Microcapsule Using Microresonators.
Dongkyu Lee 1 , Soohyoun Cho 2 , Yongbeom Park 1 , Namchul Jung 1 , Minhyuk Yun 1 , Wooree Ko 1 , Sangmin Jeon 1
1 Chemical Engineering , Pohang University of Science and Technology, Pohang Korea (the Republic of), 2 Technical Research Laboratory, POSCO , Gwangyang Korea (the Republic of)
Show AbstractWe synthesized polyurethane microcapsules containing chlorobenzene using interfacial polymerization and measured thermomechanical properties of a single microcapsule using silicon microcantilevers. A chlorobenzene-containing polyurethane microcapsule was placed on the free end of a silicon cantilever, and the temperature dependence of the resonance frequency was measured. As the cantilever was heated, the resonance frequency showed step-like increases at 109 and 270 °C due to the rupture of the capsule and the thermal degradation of the polyurethane shell, respectively. The initial mass of the single capsule was 175 ng, and this mass decreased to 30 ng after complete evaporation of chlorobenzene, indicating that the capsule consisted of 82 wt% chlorobenzene and 18 wt% polyurethane shell. The frequency changes due to the rupture of a single capsule measured by the cantilever were much sharper than the transitions measured by conventional thermogravimetric analysis (TGA), which measures the average mass change of a collection of capsules characterized by a large size distribution. When two capsules were placed on the cantilever, their individual rupture temperatures could be clearly identified. In addition, the permeability of the polyurethane shell with respect to chlorobenzene was measured, and rupture temperature was found to decrease with increasing permeability.
HH6: Poster Session
Session Chairs
Wednesday AM, December 01, 2010
Exhibition Hall D (Hynes)
9:00 PM - HH6.10
Highly Ordered Arrays of Monodisperse 2 nm Gold Nanoparticles Using Sulfonated Block Copolymers.
Hyung Min Ahn 1 , Moon Jeong Park 1 2
1 Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang Korea (the Republic of), 2 Division of Advanced Materials Science, Pohang University of Science and Technology (POSTECH), Pohang Korea (the Republic of)
Show AbstractThe development of simple and versatile methods for the preparation of nanoparticles in a size-selected and -controlled manner has drawn a great deal of attention due to their novel material properties which are greatly different from their bulk substances. Coupled with recent advances in the synthesis of nanoparticles, nanostructured organic-inorganic hybrid materials used as highly functional materials in wide varieties of applications such as optical and electromagnetic devices and metal catalysts. Particularly, a great deal of attention have been devoted to block copolymer (BCP)-nanoparticle hybrids since BCP can be self-assembled into a wide range of ordered nanostructure and nanoparticles can then be sequestered in certain domains to form ordered hybrids. In present study, gold nanoparticles have been synthesized in the ionic cluster network of polystyrenesulfonate-block-polymethylbutylene (PSS-PMB) using a liquid phase chemical impregnation/reduction process. PSS-PMB is a unique material as matrices since the chemical compositions, molecular weight, and degree of sulfonation can be easily controlled by synthetic way to yields different size and location of gold nanopatricles. At modest sulfonation levels, highly uniform gold nanoparticles with size of ca. 2 nm have been obtained. The increase in sulfonation level of PSS-PMB copolymers results in smaller (< 1.5nm) but still uniform size of the particles. Various PSS-PMB copolymers showing different morphologies have been employed for the versatile synthesis of gold nanoparticles. Transmission electron microscopy and x-ray diffraction indicate that gold nanoparticles are selectively sequestered into –SO3H groups, which do not perturb ordered morphologies of PSS-PMB matrices. Methanol oxidation properties of synthesized gold nanoparticles with various sizes and arrays are also investigated for the application of direct methanol fuel cell.
9:00 PM - HH6.11
Phenylenevinylidenebisquinolines as Indicators to Thermal Stress in Polyethylene Films.
Sofia Vazquez-Rodriguez 1 2 , Arturo Vazquez-Velazquez 1 2 , Rosa Vazquez-Garcia 3 , Virgilio Gonzalez-Gonzalez 1 2 , Oscar Coreno-Alonso 3
1 Facultad de Ingeniería Mecánica y Eléctrica, Universidad Autónoma de Nuevo León, San Nicolas de los Garza, Nuevo Leon, Mexico, 2 Centro de Innovación, Investigación y Desarrollo en Ingeniería y Tecnología, Universidad Autónoma de Nuevo León, Apodaca, Nuevo León, Mexico, 3 Centro de Investigaciones en Materiales y Metalurgia, Universidad Autónoma del Estado de Hidalgo, Pachuca, Hidalgo, Mexico
Show AbstractThe formation of excimers in polymeric films containing a fluorescent marker can be used to extract information about polymer structure promoted by heat or mechanical deformation of polymeric films. In this work, oligo(phenylenevinylidenesbisquinolines) (OPVBQ) have been prepared by mechanical milling of high energy, and incorporated to polyethylene. The OPVBQ form excimers when aggregated, and after a stimuli, the film emission is due to mixing of OVBQ into polymer matrix. Polymer films were heating from 110 °C to 130°C and quickly quenched to induce optical characteristic coming from OPVBQ excimers-monomers transition. A change in photoluminescence emission of OPVBQ appears to bear an alternative for their use as an internal strain sensor in polymer films
9:00 PM - HH6.12
Preparation and Characterization of Thermally Conductive Polymer Composite.
Sung-Goo Lee 1 , Byung Il Choi 1 , Hae Un Kim 1 , Byung Kuk Jeon 1 , Jong Chan Won 1 , Jae Heung Lee 1
1 , Korea Research Institute of Chemical Technology, Daejeon Korea (the Republic of)
Show AbstractThermally conductive polymers have been widely used for electronics, automobiles and lighting industries wherever heat is involved, while common polymers with thermal conductivity below 0.1 W/mK are regarded as thermal insulators. Thermal-conductivity-enhanced polymer composites are prepared using a melt mixing method. Polyphenylene sulfide (PPS) and polycarbonate (PC) are used as matrices, and silicon carbide (SiC), graphite and carbon fiber (C/F) are employed as thermally conductive fillers. The influence of fillers on the thermal diffusivities of polymer composites is investigated. Thermal diffusivity of the polymer composites is investigated by a Standard Laser Flash Thermal Constant Analyzer (ULVAC, TC7000). The thermal conductivity (λ) of polymer composites is calculated from the thermal diffusivity(α), density (ρ) and specific heat capacity (Cp), based on the relationship of λ=αρCp. The percolation threshold of thermal conductivity, mechanical property and morphology of polymer composites have been also discussed.
9:00 PM - HH6.13
A Hexagonal Pillar Array of Thermo-responsive Soft Actuators Prepared by Nanoimprinting.
Ching-Mao Wu 1 , Szu-Yin Lin 1 , Kuo-Tung Huang 1
1 Material and Chemical Research Laboratories, Industrial Technology Research Institute, Chutung, Hsinchu Taiwan
Show AbstractThermo-responsive actuation (thermomechanical effects) based on nematic liquid crystal elastomers (LCEs) have become a research priority in the preparation of soft actuators. Nematic LCEs combine the anisotropic features of liquid crystal phases with the rubber elasticity of polymer network. When heated at nematic to isotropic phase transition temperature (N-to-I temp), a uniaxial thermomechanical deformation of LCEs will undergo at nearly constant volume due to a change of LC director order. Recently, an array of the micro-sized LCE pillars related to such thermomechanical effects have been successfully constructed through a soft lithography technology (i.e., replica molding). The prepared LCE pillars are mono-dispersive and micro-sized. They also possess N-to-I temp higher than 100 degrees centigrade, largely limiting the available application. By contrast, the present study will report a hexagonal array of nano-sized thermo-responsive pillar actuators that are able to contract and expand in response to temperature changes around a lower N-to-I temp is manufactured via using reactive rod-like liquid crystal and ultraviolet nanoimprinting technology. According to atomic force microscope (AFM) observation, a hexagonal array of pillars can be easily constructed by nanoimprinting and a responsive surface with a thermo-stimuli-driven roughness change is achieved. The room-temperature AFM scans quantitatively represent the single pillar shows a diameter of ca. 270 nm and 140 nm in depth, and the pitch meaning the averaged inter-pillar distance is measured as ca. 425 nm, thus lying in a nano-sized range. Furthermore, temperature-variable AFM is also utilized to demonstrate the pillar behaves as a thermally-stimulated nono-sized actuator. In our case, when heated above N-to-I phase transition temperature (ca. 65 degrees centigrade), it is clearly observed that the pillar diameter is expanded in the order of 12 % and then reversibly contracted in response to temperature drop.
9:00 PM - HH6.14
Plastics that Change Physical Structure in Response to Applied Chemical Signals.
Scott Phillips 1 , Wanji Seo 1
1 Chemistry, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractThis presentation will describe a new design strategy for preparing plastics that change shape and form in response to specific external chemical signals. The plastics consist of polymers that are identical in chemical composition, but that differ in their end-capping groups and response profiles. These polymers are self-powered (i.e., they do not require addition of an external source of energy), and are capable of depolymerizing when exposed to specific chemical signals. This process of depolymerization induces changes in the shape and porosity of the plastic. Applications in the context of reconfigurable materials and point-of-care diagnostics will be presented.
9:00 PM - HH6.15
Finite Element Implementation of a Constitutive Behaviour for Shape Memory Polymers.
Enda Ryan 1 , Nathan Quinlan 1 , Mark Bruzzi 1
1 Mechanical Engineering, National University of Ireland, Galway, Galway Ireland
Show AbstractShape Memory Polymers (SMPs) are materials which can change shape when exposed to an appropriate stimulus which is usually heat. One of the most common early applications of SMPs is heat shrink tubing for electrical insulation and wire joining applications. SMPs have potential to be used in a much wider range of applications such as in medical devices and micro-mechanical devices. As a result of this, a robust understanding of the thermomechanical behaviour is required for optimised performance of such applications. Various models of SMP behaviour exist in the literature [1-4]. The constitutive behaviour of Liu et al [2] is chosen here, as it is one of the most referenced and simplest to implement. The 1-D constitutive equation for this model isσ=E(ε-εS-εT)where σ is the stress, E is the Young’s modulus and is a function of temperature, ε is the overall strain, εS is the stored strain and εT is the thermal strain. The stored strain is a term used to replicate the shape memory effect. When the material is heated and strained, an elastic stress exists in the material. Upon cooling in this strained state some of the strain is “frozen”. This increases εS which decreases σ. When heated again the strain is released by decreasing εS and the material recovers its’ original shape. This model was implemented using the ABAQUS user subroutine UMAT. Material properties were obtained by tensile testing of an SMP sample in a DMTA. A DMTA was also used to test the predictions of the model. The SMP model has been implemented in 3-D. This model reproduces the behavior of a SMP as it goes through a complete thermomechanical cycle. The model has been used to model the behaviour of heat-shrink tubing. The model offers scope to create an accurate thermomechanical model of SMPs which would be of great use to many industries. It also shows that these materials can be modelled using FEA in ABAQUS which will make modelling their interactions with other materials more straightforward.References[1] Tobushi H., Okumura K., Hayashi S., Ho N., ‘Thermomechanical constitutive model of shape memory polymer’, Mech. Mat. 33, 545-554 (2001).[2]Liu Y., Gall K., Dunn M.L., Greenberg A.R., Diani J., ‘Thermomechanics of shape memory polymers: Uniaxial experiments and constitutive modelling’. Int. J. Plast. 22 279-313 (2006).[3]Kafka V., ‘Shape memory polymers: A mesoscale model of the internal mechanism leading to the S.M. phenomena’, Int. J. Plast., 24 1533-1548 (2008).[4]Barot G., Rao I.J., ‘Constitutive modelling of the mechanics associated with crystallisable shape memory polymers’, Z.A.M.P. 57 652-681 (2006).
9:00 PM - HH6.16
Functionalized Polymer Membranes for Taste Sensing.
Basudam Adhikari 1
1 Materials Science Centre, Indian Institute of Technology, Kharagpur, West Bengal, India
Show AbstractThere are reports of fabrication of taste sensors by incorporating lipids in PVC matrix or adsorbing lipids into Millipore filter paper. We have prepared taste sensor material without using any lipid by functionalizing the polymers. Maleic acid cross-linked and phosphorylated polyvinyl alcohol (PVA), phosphorylated commercial cellophane, phosphorylated PVA-cellulose composite, polyacrylic acid grafted cellulose and polyacrylamide grafted cellulose membranes were prepared for use as functionalized membranes for sensing of tastes of sweetness, saltiness, sourness, bitterness and umami (the taste of nonveg foods). Cross-linked polyvinyl alcohol, commercial cellophane and PVA soaked cellulose were phosphorylated with POCl3. The membrane was characterized by water and moisture absorption studies and contact angle measurement to have an idea about the hydrophilicity of the polymer membrane. Spectroscopic analysis was done to have an idea of the chemistry of the membrane surface. Morphology of the membrane surface was done by XRD analysis and microscopy was done. Surface charge density of the membrane was also measured. The taste response measurement in terms of electric potential was done using a potentiometric electrochemical device. The sensor characteristics like temporal stability, response stability, response to different taste substances and reproducibility of sensing performance were studied using the above-mentioned membranes. The time required by the membrane to attain temporal stability ranged from 7- 30 mins. Stability in response in the five basic taste substances for the period of 5 min was quite good. The membranes also showed good reproducibility in response with small drift in potential. Sensor devices prepared with these membranes have shown distinct response patterns for different taste substances in terms of membrane potential. Membranes showed varied response patterns to different taste substances. But membranes did not show significant change in potential due to change in concentrations of sucrose. Threshold concentrations of the membranes for HCl, NaCl, quinine-hydrochloride (Q-HCl), sucrose, monosodium glutamate (MSG) are below human threshold concentrations. Sensor devices prepared with these membranes have excellent shelf life. Membranes also showed characteristic response patterns for organic acids like acetic acid, citric acid, formic acid etc., mineral acids like HCl, H2SO4 and HNO3 salts, bitter substances, sweet substances and umami substances. All the membranes showed some recognition ability to different taste substances.
9:00 PM - HH6.18
Polymer Thin-films as an Anti-angiogenic and Neuroprotective Biointerface.
Rahul Ahuja 1 , Balaji Nithianandam 4 2 , Tomoki Kurihara 2 , Magali Saint-Geniez 2 , Patricia D’Amore 2 , Stephen Redenti 3 2 , Michael Young 2 , Sarah Tao 1
1 , Draper Laboratories, Cambridge, Massachusetts, United States, 4 Molecular and Cellular Physiology, University of Cincinnati , Cincinnati, Ohio, United States, 2 , Schepens Eye Research Institute, Boston, Massachusetts, United States, 3 Biological Sciences and Biochemistry, City University of New York, Lehman College, Manhattan , Massachusetts, United States
Show AbstractThe wet form of age-related macular degeneration (AMD) is an ocular pathology that is characterized by the growth of leaky new vessels beneath the retina. The abnormal new vessels damage the retinal pigment epithelium (RPE), and consequently the neural retina, leading to the loss of central vision. To limit neovascularization and confer neuroprotection, a novel thin-film polycaprolactone (PCL) implant was designed to provide a local sustained delivery of pigment epithelial derived factor (PEDF), an anti-angiogenic and neurotrophic protein, to the subretinal space. PCL is a polymer that degrades slowly while maintaining its structural integrity, making it an ideal material candidate for long-term therapeutic release of proteins. A microemulsion of either PEDF or a model protein, FITC-albumin, in PCL was formed into a thin (less than 10μm) film by a modified spin-assisted solvent casting method. The FITC-albumin was successfully encapsulated in 100μm diameter microreservoirs within the PCL film. After an initial burst over the first 48 hours, the 78mm2 PCL thin-film demonstrated sustained release at a rate of 8ng/hour for 8 days. This was followed by another 48-hour burst release phase and a 3.3ng/hour sustained release phase for 6 days. After one week it was estimated that 7.4% of the total PEDF content was released. The PCL thin-film with encapsulated PEDF was found to be both neuroprotective and anti-angiogenic in vitro. This PCL-PEDF thin-film composite reduced the proliferation of cultured human umbilical vein endothelial cells (HUVECs) by approximately 65% (p<0.01) compared to HUVECs in standard culture. Moreover, the PCL thin-film increased the survival of photoreceptor cells isolated from C57BL/6 wild type mice by approximately 150%. These results demonstrate that controlled delivery of PEDF from PCL films provides both an anti-angiogenic and neuroprotective interface, and may provide a novel therapeutic strategy for the treatment of wet AMD.Copyright 2010 by The Charles Stark Draper Laboratory, Inc. all rights reserved
9:00 PM - HH6.19
Aromaticity in Mechanophores a New Method Toward Generating Acids Using Mechanochemistry.
Brian Steinberg 1 2 , Jeffrey Moore 1 2
1 Material Science and Engineering, Beckman Institute for Advanced Science, Urbana, Illinois, United States, 2 Chemistry, University of Illinois at Urbana Champaign, Urbana, Illinois, United States
Show AbstractForce-sensitive molecules also known as mechanophores have captured a great deal of attention due to their potential application in stress-sensing and autonomic healing materials. Mechanical activation is achieved by applying directional forces to the polymer bound mechanophore. To meet the force requirements for activation it is often necessary to incorporate the mechanophore into the polymer using a chain center polymer geometry. While this approach is effective for testing and developing mechanochemical activity the mechanophore to polymer ratio is limited. A primary goal leading to bulk mechanochemical transformations will require multiple mechanophores to be incorporated throughout an entire polymer chain with high fidelity. We have now adopted this approach by developing a mechanophore monomer unit, which upon polymerization provides a fully integrated mechanophore based polymer. The mechanophore monomer takes advantage of a latent aromatization element buried within its core, such that upon activation the mechanophore yields not only a new fully aromatized subunit, but also quantitative release of an acid.
9:00 PM - HH6.2
Chitosan/Heparin Hydrogel Containing Basic Fibroblast Growth Factor for Cell Encapsulation.
Hyuksang Yoo 1 , Ji Suk Choi 1 , Shinyoung Park 1 , Hye Sung Kim 1 , Young Ju Son 1
1 , Kangwon National University, Chuncheon Korea (the Republic of)
Show AbstractControlling release of growth factors from hydrogels has been challenging because encapsulated proteins often showed initial burst release profiles due to fast diffusion process. Heparin enhances a half-life and activity of bFGF, also, protects bFGF from inactivation by acid and heat. In this study, biodegradable hydrogel (22%, w/w) composed of Di-acrylated Pluronic F127 and glycidyl methaacrylated chitooligosaccharide (COS) (0, 20, and 50%, w/w) was prepared in an aim to control release of bFGF. A photo-initiator, Irgacure2959 (0.01%, w/w), was added to the polymer mixture. In order to measure mechanical property of the hydrogel, the hydrogels were monitored using a rotating rheometer. The amount of released bFGF from the hydrogels was quantitatively determined by ELISA. Human dermal fibroblasts cultivated in the hydrogel to measure cyto-toxicity of the hydrogel by MTT assay. In order to determine degradation rates and rheological property of chemically-crosslinked Pluronic F127/COS hydrogels containing bFGF/heparin, elastic modulus of the Pluronic F127/COS hydrogels was monitored. When blend ratio of COS increased, a stiffness of the hydrogel increased and a degradation rate of the hydrogel decreased. When a content of COS was 50%, w/w, cell proliferation was higher than 0 and 20%, w/w of COS. Because Pluronic F127 what has cyto-toxicity property was decreased. Mechanical property and biocompatibility of COS/heparin hydrogels were improved by increasing a content of COS. Therefore, the chemically-crosslinked hydrogels containing bFGF/heparin can be a superior candidate for tissue engineering scaffold.
9:00 PM - HH6.20
A Patterned Conducting Polyaniline Layer on a Non-conducting Polymer Matrix.
Edward Song 1 , Jin-Woo Choi 1 2
1 Department of Electrical and Computer Engineering, Louisiana State University, Baton Rouge, Louisiana, United States, 2 Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, Louisiana, United States
Show AbstractPolyaniline is one of the most studied conducting polymers and its properties have been used in many sensor applications including gas sensors and pH sensors. In this work, we present a method that is able to embed a conducting polyaniline film in a desired pattern onto a non-conducting polymer matrix. We have developed an embedded polyaniline film on a polydimethylsiloxane (PDMS) matrix using a cast molding technique. The polyaniline film was grown by electrochemically polymerizing polyaniline from an electrolyte containing sulfuric acid and aniline monomer. A three-electrode cell system was used with a standard Ag/AgCl reference electrode, a gold auxiliary electrode, and a patterned gold working electrode. After the polyaniline film was formed on the patterned working electrode, PDMS was poured atop and cured. Cured PDMS was then debonded along with the polyaniline film embedded on the PDMS layer or block. The gold layer of the working electrode can be patterned using a photolithography steps so that the designed pattern can be transferred by the polyaniline growth on the working electrode. The greenish color of the polyaniline film indicated that the embedded polyaniline was in the conducting state (emeraldine form) and the conductivity of the polyaniline has also been verified by applying a DC voltage across the film and measuring the current through the polyaniline layer. The advantage of this technique is that the PDMS matrix holds the polyaniline in place while allowing the polyaniline film to undergo reversible doping/dedoping chemistry when electrolyte solution comes into contact with the surface of the film. The developed technology can be used for various chemical sensor applications, for example, a pH sensor or gas sensors where a flexible and all-polymer apparatus is needed. Process optimization and further electrochemical characterization of the patterned and embedded polyaniline layer is currently underway.
9:00 PM - HH6.21
Nanocomposite Electrolytes Based on Polyethylene Glycol and Titanium Oxide Compounds for Electrochromic Applications.
Narcizo Mendoza 1 2 , Liliana Hechavarria 1 , Francisco Paraguay 2 , Hailin Hu 1
1 Solar Materials, Centro de Investigacion en Energia, UNAM, Temixco, Morelos, Mexico, 2 , Centro de Investigacion en Materiales Avanzados, Chihuahua, Chihuahua, Mexico
Show AbstractLow molecular weight polyethylene glycol (PEG, 600) is a good solvent-free viscous ionic conductor. With a lithium salt concentration of 1:8 between lithium and ether oxygen molecule, the conductivity of the PEG-Li+ electrolyte can be larger than 10-4 Scm-1 at room temperature. By using this electrolyte, tungsten oxide (WO3) based electrochromic devices (ECDs) have been prepared and exhibited a good optical contrast at the wavelength range from 2500 to 300 nm. However, the color change is quite slow in these devices when the applied potentials are switching between + 1V and -1.5 V. To improve the electrochromic performance of polymeric electrolyte based ECDs, nanocomposites of PEG-titanium oxide compound have been prepared by sol-gel method. Transmission Electronic Microscope (TEM) images of the composite samples show nanometer size of titanium oxide compounds inside the PEG matrix. The formation of new association between PEG and titanium oxide compound is confirmed by thermogravimetric analysis (TGA) and Fourier Transform Infrared Spectroscopy (FT-IR). The electrochromic response of WO3 with PEG-TiO2 – LiI as electrolyte is considerably improved under the same potential polarizations. It is also observed that the source of lithium salt play an important role in the redox process of the devices. The mechanisms of charge separation and storage in the nanocomposite electrolytes as well as the charge transfer at the electrolyte/WO3 film interface have been proposed and supported by electrochemical impedance spectroscopy study on the mentioned ECDs.
9:00 PM - HH6.22
Bimolecular Recombination and Space Charge in P3HT:PCBM Solar Cells.
Feng Gao 1 , Jianpu Wang 1 , Neil Greenham 1
1 Department of Physics, University of Cambridge, Cambridge United Kingdom
Show AbstractDrift-diffusion modeling is a useful tool to disentangle the different transport and recombination processes that determine the performance of organic photovoltaics. In the modeling, the carrier mobility is an important parameter, and it has recently been appreciated that it is important to include the dependence of mobility on carrier density in order to accurately model the performance of organic devices. In this work, we determine the dependence of the charge carrier mobility on temperature, carrier density and the electric field in P3HT-PCBM bulk heterojunction organic solar cells. Based on these parameters, experimental current-voltage characteristics over a wide range of light intensities and temperatures can be modeled. The inclusion of the carrier-density dependence is particularly important at low temperatures and at high intensities. From the model, we are able to quantify the relative contributions of bimolecular and geminate recombination, and to assess the importance of space-charge effects in the devices.
9:00 PM - HH6.23
Robust Low Refractive Index Optical Film Based on Spin-on Organosilicate.
Yoichi Taira 1 , Kuniaki Sueoka 1 , Hidetoshi Numata 1 , Geruad Dubois 2 , Willi Volksen 2
1 , IBM Research - Tokyo, Yamato Japan, 2 , IBM Research - Akmaden, Sab Jose, California, United States
Show AbstractSol gel material can have a low electrical susceptibility because of its low density. Nanoporus oiganosilicate has been studied as the dielectric layer material of the CMOS wiring levels. Usually the mechanical toughness decreases rapidly as we lower the material density. However, the ethylene bridged oxycarbosilene (Et-OCS) organo-silicate glass has been shown to have a high fracture toughness even when the density is lowered If we can make the nanopores of this material system small and uniform enough, the material can be transparent enough in the visible region. If we can realize a low enough index of refraction, the system will have a new optical applications such as in lightings and displays. Presently the index of refraction of robust solid material is larger than 1.29, which is the case of amorphous fluorocarbon polymer. We could evaluate the optical properties of en Et-OCS organosilicate thin film. The sample was deposit by spin coating on a quartz plate and processed at 400 C. The sample is 600nm thick and uniformly transparent. No visible light scattering was observed. The refractive index of the film was determined to be 1.20 at 633nm by measuring the critical angle of refraction. The film was robus enough and did not break during the measurement where adhesive film was attached onto the surface. Since the material density can be further reduced, we may be able to lower the refractive index further. The low refractive index film has an immediate application in the backlight system used in liquid crystal display systems. A thin low index layer with an appropriate index can be used to realize a highly collimated backlight system without a loss.
9:00 PM - HH6.24
Chemically Synthesized Transparent Graphene/ Polyaniline and Polythiophene Nanocomposites Film as Counter Electrode for Efficient Dye-sensitized Solar Cells.
Farah Alvi 1 2 , Manoj Ram 2 3 , Stefanakos Lee 1 , Ashok Kumar 2 3
1 Electrical Engineering, University of South Florida, Tampa, Florida, United States, 2 Nanotechnoloy research and Education Center, University of South Florida, Tampa, Florida, United States, 3 Mechanical Engineering, University of South Florida, Tampa, Florida, United States
Show AbstractIn recent years, there has been considerable interest amongst researchers to develop novel inorganic-organic hybrid materials for wide scale photovoltaic’s application. A dye-sensitized solar cell (DSCs) has become one of promising choices for energy application due to their low production costs and the relatively high photo-voltaic performance. In DSCs, platinum (Pt) is generally used as counter electrode. However, it isn’t suitable for large scale production because Pt is not only rare metal but also expensive. Here we report the novel graphene –conducting polymer nanocomposites by wet chemical techniques which has been proved as a simple and inexpensive strategy with good catalytic activity for the reduction of trioxide ion alternative to Pt.These conducting polymer-(polyaniline (PANI) and polythiopnene(PTh) graphene nanocomposites have been used as counter electrodes in dye-sensitized solar cells yielding a power conversion efficiency, close to the classical platinum coated counter electrode. In this work, initially we have prepared `gaphene- PANI and graphene-PTh nanocomposite films by wet polymerization method. Following this, conduting polymer-graphene nanocompsites films were characterized by UV-Vis, FTIR, cyclic voltammetry, impedance, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and electrical conductivity. Results have confirmed the super conducting behavior of graphene-PANI and graphene-PTh composites for energy application. Further, results indicated that gaphene- PANI and graphene-polythiophene films have exhibited wide potential window. Moreover photoelectrochemical behavior of gaphene- PANI and graphene-PTh revealed the faster and two fold current than the graphene films. The results confirmed that the gaphene- PANI or graphene-PTh system has wide potential applications in the design of photovoltaic and electrochemical capacitors.
9:00 PM - HH6.3
Photo-removable Polymer Brush for Protein Patterning.
Yosuke Hoshi 1 , Youyong Xu 1 , Christopher Ober 1
1 , Cornell University, Ithaca, New York, United States
Show Abstract Patterning of biomolecules, especially proteins and antibodies, has been widely investigated because of its utility for biological applications such as biosensors. A polymer brush prepared by surface-initiated ATRP (SI-ATRP) is a powerful platform for controlling the interaction between biomolecules and surfaces. Some methods, such as photolithography using conventional photoresist or microcontact printing, have been reported. As the semiconductor industry works to add diverse functions to ICs, following the so called “more than Moore” approach, and the bio-chip is an application of great interest. To fabricate bio-chip embedded in ICs, a new integration process which is both biocompatible and compatible with current semiconductor processes is required. In this work, we introduce a new SI-ATRP initiator which contains o-nitrobenzyl ester as a photoreactive group. This initiator enables us to prepare various polymer brushes on silicon oxide by ATRP reaction, and to pattern these brushes by irradiation with 365nm UV light. After the removal of the polymer brush, hydroxyl groups are formed on the exposed area which is useful for further functionalization. As confirmation of this strategy, a multicomponent polymer brush was prepared and a protein was bound on it to form a patterned protein surface. This process can be done in mild and wet condition and does not require any special equipment. In summary it is a simple and versatile patterning method.
9:00 PM - HH6.30
Hybrid Polyurethane Nanocomposites: Synthesis and Microstructure.
Estefania Huitron-Rattinger 1 2 , Kazuki Ishida 3 , Angel Romo-Uribe 2 , Patrick Mather 3
1 Posgrado de Ingenieria, Facultad de Quimica, Universidad Nacional Autonoma de Mexico, Cuernavaca, Morelos, Mexico, 2 Instituto de Ciencias Fisicas, Universidad Nacional Autonoma de Mexico, Cuernavaca, Morelos, Mexico, 3 Syracuse Biomaterials Institute and Department of Biomedical and Chemical Engineering, Syracuse University, Syracuse, New York, United States
Show AbstractWe have synthesized a series of cationic polyurethane nanocomposites incorporating the inorganic-organic hybrid moiety, polyhedral oligomeric-silsesquioxane (POSS), alternating in a multiblock fashion with a biodegradable polycaprolactone backbone. It was hypothesized that the combination of ionic groups and multiblock architecture would lead to rich, perhaps competing, nanostructures. Average molecular weights ranged from 20,000 to 200,000 g/mol and the microstructure at the molecular- and nano-scales were investigated via wide-angle and small-angle X-ray scattering (WAXS and SAXS, respectively). The microstructure was correlated with the thermal properties, as determined by differential scanning calorimetry (DSC), and with the dynamic mechanical properties, determined via dynamic mechanical analysis (DMA). DSC data showed that melting transition temperature (Tm) of PCL is significantly reduced from that of neat PCL as the concentration of chain extenders was increased. Also, for each series of materials the heat of crystallization, delta Hc, due to the PCL crystalline phase, decreased as POSS content was increased. Thermogravimetric analysis (TGA) data showed that there is higher thermal stability for those nanocomposites that bear higher POSS content. As the bulk properties are a result of the micro and nanostructure in materials, WAXS and SAXS was applied to investigate in detail the microstructure. Wide-angle X-ray scattering showed the existence of crystalline reflections due solely to PCL at low concentrations of POSS. However, as the concentration of POSS increased (up to about 20 mol-%) crystalline reflections associated with POSS and PCL crystals emerged. On the other hand, SAXS showed long range order in the PUs due to PCL lamellar morphology. Increasing the concentration of POSS produced a second intensity maximum in the SAXS trace indicating the presence of POSS clusters in addition to the PCL crystalline regions. The different crystalline forms of POSS and PCL for each composition allowed for tailored thermal transitions, opening up the thermal activation mechanism to produce shape memory behavior in these materials.
9:00 PM - HH6.4
Realization of Shape-governed Pattern Formation in Belousov-Zhabotinsky Self-oscillating Gels.
Irene Chen 1 , Olga Kuksenok 3 , Victor Yashin 3 , Anna Balazs 3 , Krystyn Van Vliet 2
1 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Chemical Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 Materials Science & Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThe majority of "smart polymers" are designed to respond only once to external stimuli and are not able to maintain autonomous, cyclic responses. In contrast, polymer gels that incorporate the Belousov-Zhabotinsky (BZ) reaction are capable of undergoing self-oscillating changes in both volume and color for extended durations in a stationary solution. Computational models of these BZ gels have predicted that oscillating patterns can be modulated by changing the physical shape and size of the polymer gels. While materials that exhibit such shape-dependent patterns introduce new applications for chemomechanical sensors and biological analogues, they have not been demonstrated experimentally. Here, we present the first experimental validation of the predicted shape-dependent pattern formation resulting from the periodic reduction and oxidation of the BZ catalyst. This study shows how the complex, spiral wave patterns observed within BZ gels can be harnessed and controlled by varying the gel’s dimensions. We explore the effects of gel aspect ratio and absolute dimensions, both for N-isopropylacrylamide gels containing covalently bound catalyst and for polyacrylamide-silica gel composites containing physically associated catalyst. Our results demonstrate that patterns in self-oscillating BZ gels evolve over hours of reaction time. At early reaction times, pattern formation depends strongly on gel size, shape, and random perturbation in the initial conditions, whereas at late reaction times, this pattern formation becomes independent of gel dimensions (for the gel sizes considered here). We further show that these "smart gels" can be recycled, in that the same gel can undergo the BZ reaction multiple times without change in pattern formation or period of oscillation. Lastly, we confirm that the BZ gel exhibits synchronized chemomechanical coupling in which autonomous volume changes occur in conjunction with oscillating chemical changes, provided that all gel dimensions are less than the critical lengthscale of the reaction. Thus, such shape- and size-dependent modulation of chemomechanical swelling can enable new applications for BZ gels.
9:00 PM - HH6.5
Piezoelectricity and Mechanical Properties of Electrospun PVDF Nanofiber.
Pei Chen 1 , Shane Hague 1 , Qian Li 1 , Shing-Chung Wong 1
1 Mechanical Engineering, University of Akron, Akron, Ohio, United States
Show AbstractPolyvinylidene Fluoride(PVDF) is well known for its piezoelectricity. Current applications of PVDF are mostly in the form of films. In this study, PVDF nanofiber was prepared by electrospinning technique, and piezoelectricity of PVDF nanofiber was characterized by examining signal nanofiber. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and fourier transform infrared spectroscopy (FTIR) results showed that the electrospinning process increased the crystallinity and beta-phase crystal compared to PVDF film, as beta-phase is primarily responsible for the piezoelectrical property of PVDF. By adjusting electrospinning process parameters, PVDF nanofibers with different diameters were prepared. Mechanical properties were studied by tensile testing signal PVDF nanofiber. Increased tensile strength and modulus were observed by decreasing fiber diameter from 2000 nm to 100 nm, and an abrupt increase was observed at ~400 nm.
9:00 PM - HH6.6
Alternating Encapsulation in Multi-nozzle Electrospinning Systems.
Nae-oh Chung 1 , Chul Ho Park 1 , Jonghwi Lee 1
1 , Chung - ang Univ., Seoul Korea (the Republic of)
Show Abstract Encapsulation is important in many applications such as drug delivery, cosmetics, foods, electronics, membrane, etc. Recently, we reported novel alternating encapsulation by multi-nozzle electrospinning by employing side-by-side inner nozzles (core) in an outer nozzle (shell). In this preparation technique, there are many variables of fluid dynamics and electro hydrodynamics to predict the results and related mechanism, which mostly remain uninvestigated. Herein, we investigated the effect of nozzle configuration (single, twin core, etc) on alternating encapsulation. Polyvinyl alcohol, Pluronic F-127, and poly(vinylidene fluoride) were used as core materials, and polystyrene was used as a shell materials. The morphology investigated by SEM, optical, and confocal microscopy showed the successful alternating encapsulation of inner materials inside polystyrene fine fibers. The tendency of alternating encapsulation depends on conductivity, viscosity, and the number of core nozzles. The polymer solutions, which are not spinnable using a single nozzle electrospinning, could be spun through inner nozzles, and their alternating encapsulation was possible. Also, we could make the chopped fibers of poly(vinylidene fluoride), as using twin core system of this method. Interestingly, the polystyrene solution used as a shell fluid could not be stably encapsulated by the same polystyrene shell solution. Alternating encapsulation by multi-nozzle electrospinning systems appears to result from the competition between the inner nozzles. This unique preparation method could break the current limitations of possible morphology of 1D structure.
9:00 PM - HH6.7
Surface Functionalization of Electrospun PET Fibers with Polymer Brushes.
Kristen Roskov 1 , Ali Evren Ozcam 1 , Jan Genzer 1 , Richard Spontak 1 2
1 Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractElectrospinning polymers yields micro/nanofibers ranging in diameter from 450 to 1200 nm, thereby providing a viable means by which to generate nonwoven porous webs for use in, for example, filtration applications. Most homopolymers employed in electrospinning are selected for their spinnability and resultant mechanical stability, but contemporary applications often require specific surface functionality. In this work we consider the growth of polymer brushes on electrospun microfibers of poly(ethylene terephthalate) (PET), a linear, aromatic polyester that is known for its structural and mechanical strength. While surface graft polymerization on flat polymer surfaces has been reported with a variety of functional monomers, we aim to achieve comparable results on electrospun fibers. Electrospun PET fiber surfaces are first modified via the amidation reaction of the amine group on aminopropyl triethoxysilane (APTES) with the ester groups on PET, followed by the subsequent growth of functional polymer brushes measuring ~40 nm (dry) composed of poly(N-isopropylacrylamide) (PNIPAAm), 2-hydroxyethylmethacrylate (PHEMA) or 2-(dimethylamino)ethylmethacrylate (PDMAEMA) via atom transfer radical polymerization. X-ray photoelectron spectroscopy is used to measure the surface concentrations of nitrogen, carbon and oxygen on the fibers before and after polymer brush growth. Measured concentrations agree favorably with calculated values and suggest that polymer brushes cover the PET surfaces uniformly. Specifically, electrospun mats modified with PNIPAAm brushes have been exposed to a suspension of gold nanoparticles at temperatures above and below the lower critical solution temperature of PNIPAAm (32°C) to probe the effect of nanoparticle absorption on brush conformation. Experimental observations by scanning electron microscopy indicate that the concentration of nanoparticles bound to the fiber surface depends sensitively on temperature. In addition, nitrogen concentration measurements from XPS show a reduction in protein adsorption upon introduction of PHEMA brushes on both flat and fiber samples. Moreover, quarternization of PDMAEMA brushes grown on PET fibers with alkyl bromides differing in methylene length results in polycationic brushes that impart antibacterial properties against organisms such as E. coli. These functional fibers can be used as advanced materials in a wide variety of technologies such as affinity filters, wound dressings and antibacterial textiles.
9:00 PM - HH6.8
Photo-response Behavior of Electrospun Nanofibers Based on Spiropyran-Cyclodextrin Modified Polymer.
Frederico De Sousa 1 2 , Joao Guerreiro 2 3 , Minglin Ma 4 , Daniel Anderson 4 , Chester Drum 2 , Ruben Sinisterra 1 , Robert Langer 2
1 Department of Chemistry, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil, 2 Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Institute for Biotechnology and Bioengineering, Center for Biological and Chemical Engineering, Instituto Superior Técnico, Lisboa Portugal, 4 David H. Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractTunable and durable photochromic materials are a rapidly expanding area of interest in application ranging from biomedical devices to industrial-fields. Here we examine electrospun poly (methacrylic acid) PMAA nanofibers covalently modified with the highly photochromic molecule, spiropyran (SP) or a derivate SP which is firstly coupled to a cyclodextrin molecule (βCDSP). The photochromic properties of the starting materials and of the nanofibers were investigated. βCDSP, PMAASP and PMAA-βCDSP polymers exhibited a reverse photochromism. The kinetic results investigated using UV-visible spectroscopy revealed a faster isomerization process for the βCDSP molecule, than that for the PMAA-βCDSP and for the PMAASP, the slowest one. The fastest isomerization is attributed to the presence of a large number of hydroxyl groups of the βCD which stabilizes the merocyanine form via hydrogen bonding and the slowest isomerization is related to the PMAA chain structure that stabilizes the spiropyran form. Thus, combining the PMAA and βCD properties the photo-isomerization can be modulated. The photo-reversibility of this material was verified by UV-visible measurements cycling visible and UV light several times. Infrared spectroscopy (FTIR-ATR) and water contact angle were used for the nanofiber surface characterization, demonstrating the presence of the spiropyran on the mats surface and also showing a minimal effect on nanofiber size and shape when compared to PMAA fiber.
9:00 PM - HH6.9
Instant Deformation of Metal-sputtered Micron Polymer Wire Actuators.
Jianxia Zhang 1 , John Wiley 1
1 AMRI/Chemistry, University of New Orleans, New Orleans, Louisiana, United States
Show AbstractDispersed micron-sized polymer wires, fabricated by bulk polymerization in Glass Capillary Array (GCA) templates, were coated with silver metal on one side. On introduction of the appropriate solvent (e.g. dichloromethane), wires swell asymmetrically. Through proper control of the thickness of silver, wires can be made to instantaneously bend to form various shapes including rings and spirals. In contrast, for thicker metal coatings, little or no bending occurs, and for thin metal coatings, as wires start to curl, the metal coating can break such that the wire immediately springs back to its original linear conformation. Details on the preparation and characterization of these wires will be presented along with a discussion of the potential application of these unusual actuating systems.
Symposium Organizers
Zhongyang Cheng Auburn University
Vivek Bharti 3M Company
Zhuo Xu Xi’an Jiaotong University
Debra A. Wrobleski Los Alamos National Laboratory
HH7: Shape Memory Polymers and Thermal Effect
Session Chairs
Wednesday AM, December 01, 2010
Back Bay B (Sheraton)
9:30 AM - **HH7.1
Shape Memory Polymers: New Phenomena and Applications.
Tao Xie 1
1 , General Motors R&D Center, Warren, Michigan, United States
Show AbstractA shape memory polymer traditionally refers to a polymer that can memorize one temporary shape and recover to its permanent shape upon exposure to an external stimulus. Although this basic concept has been known for at least half a century, recent advances within the last five years have led to the discoveries of previously uncovered memory properties that challenge such a traditional concept. In this talk, I will give a brief overview of how the shape memory polymer field has evolved scientifically and what the progress means for practical applications (e.g. reversible adhesive systems and self-healing materials).
10:00 AM - HH7.2
Thermo-mechanical Behavior of (Meth)Acrylate Shape Memory Polymer Networks.
Carl Frick 1 , Nishant Lakhera 1 , Christopher Yakacki 2 3
1 Mechanical Engineering, University of Wyoming, Laramie, Wyoming, United States, 2 , MedShape Solutions, Inc., Atlanta, Georgia, United States, 3 School of Materials Science and Engineering, The Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractShape memory polymers (SMPs) have attracted increased attention over the last several years due to their ability to temporarily store a deformed shape, and subsequently recover the deformation upon exposure to heat. This capability has led to several proposed applications, including self-deployable structures for biomedical and space applications, among others. Inherent advantages include high recovery strain, low density, and low cost. Because the shape-memory effect in polymers is not an intrinsic material property, but rather relies on polymer microstructure and thermo-mechanical processing, researchers have shown that various types of polymers can be used as SMPs. Polymers capable of solidification upon exposure to ultra-violet light (e.g. photopolymers) have several inherent advantages including the possibility of in situ fabrication, relatively quick synthesis rates, and simple one-step processing into complex geometries. A subset of photopolymers, (meth)acrylate-based networks, are advantageous because their material properties can be tuned by control of polymer chemistry. Tailoring of mechanical properties is critical to match the needs of a specific application.Our overall approach is based on developing a photocrosslinkable polymer network with a favorable shape-memory response, using polymer chemistry and crosslinking density to control thermo-mechanical properties. Three polymer networks were created and thermo-mechanically tested, each from tert-Butyl acrylate linear builder co-polymerized with a Poly(ethylene glycol) dimethacrylate cross-linker. By systematically altering the molecular weight and the weight fraction of the cross-linker, it was possible to create three polymers that exhibited the same glass transition temperature, but varied by almost an order of magnitude in rubbery modulus. Therefore, the mechanical stiffness could be tailored to suit a given application. Recovery behavior of the polymers was characterized through Free-Strain, Fixed-Stress, and Partial recovery testing over a range of deformation temperatures. Previous studies have implicitly assumed a linear relationship between Free-Strain (i.e. no actuation force) and Fixed-Stress (i.e. maximum actuation force), however, this has never been shown experimentally. Our stress-strain testing have directly shown that the actuation force is strongly dependent on the temperature at which the material is initially deformed, as well as the amount it is partially constrained. Specifically, specimens deformed at temperatures below the onset temperature demonstrate Fixed-Stress and Partial recovery values 300-500% larger than specimens deformed above the glass transition temperature. The polymer networks investigated in this study have been proposed for use in biomedical applications, which are subject to partially constrained recovery conditions in vivo. This work helps better understand the recovery behavior under these conditions.
10:15 AM - HH7.3
Impact of the Deformation Temperature on the Properties of Shape Memory Epoxy Networks.
Ingrid Rousseau 1 , Diane Feldkamp 1
1 Chemical Sciences and Materials Systems Lab, General Motors Company, Warren, Michigan, United States
Show AbstractWhile epoxy resins remain infrequently used as shape memory polymers (SMP’s), they are a promising base material for highly demanding applications due to their intrinsic physical properties and ease of processing. Although proven to show excellent shape memory effect in a previous study, the main disadvantage of epoxy SMP’s resides in their intrinsically low ultimate strains, which translates to reduced deformation strains compared to conventional SMP’s. Here, we show the impact of the deformation conditions, specifically the temperature, on the shape memory (SM) behavior and characteristics of epoxy SMP’s. By simply varying the temperature during deformation (i.e., the programming step of the shape memory effect), the ultimate strain of the SM epoxy was improved three- to five-fold, thereby providing for an increased range of reachable deformation strains during shape memory thermo-mechanical cycling. This research unveils newly developed epoxy-based SMP’s with improved deformability range and high strength with intrinsically good thermal and chemical stability.
10:30 AM - HH7.4
Effect of Smectic Layer Interdigitation on Shape Memory Properties for Side-chain Liquid Crystalline Polymer Networks.
Suk-kyun Ahn 1 , Prashant Deshmukh 2 , Rajeswari Kasi 1 2
1 Institute of Materials Science Polymer Program, University of Connecticut, Storrs, Connecticut, United States, 2 Department of Chemistry, University of Connecticut, Storrs, Connecticut, United States
Show AbstractShape memory polymers (SMPs) are a class of stimuli-responsive materials which have an ability to recover their permanent shape from the temporary shape when exposed to external stimuli such as heat or light. SMPs have received increasing attention due to their potential applications for intelligent biomedical devices including sutures, stents as well as smart functional devices such as sensors, fabrics and fasteners. Here, we report a new class of side-chain liquid crystalline networks (SCLCNs) bearing cholesteryl mesogens and investigate their structure-property relations and corresponding shape memory properties. The SCLCN consisted of three monomers, 5-{n-(cholesteryloxycarbonyl)-pentadecyloxycarbonyl}-bicyclo[2.2.1]hept-2-ene (NBCh-n), 5-(acryloyl butoxycarbonyl)-bicyclo[2.2.1]hept-2-ene (NBBA), and poly(ethylene glycol) functionalized norbornene (NBPEG), is prepared by ring opening metathesis polymerization (ROMP), followed by thermal cross-linking at 120 oC. Each monomer functions specific roles in the SCLCNs: (1) NBCh-n provide LC properties, (2) NBBA is a cross-linkable unit, and (3) NBPEG performs as a plasticizer. The mesomorphic structure of the SCLCNs determined by X-ray diffraction (XRD) is smectic A (SmA) where their microstructures are varied from bilayer, mixed layer and single layer depending on their flexible spacer length between polymer main-chains and cholesteryl side-chains.Shape memory properties of the SCLCNs are characterized by dynamic thermomechanical analysis (DMA). A glass transition (Tg) and a clearing transition temperature (Tcl) in the SCLCNs are used as dual molecular switches, which allow for exerting multiple shape memory effects including one-way (1W), two-way (2W)shape memory and tripe shape effect. In particular, we demonstrate that the microstructural changes in the SCLCNs arising from the interdigitation of cholesteryl side-chains significantly influence final shape memory properties. The understanding the shape memory mechanisms of the new class of our SMPs will be crucial to broaden the fundamental knowledge in the field of smart materials. Furthermore, our SMPs will also have a significant impact for the applications including thermal actuators and biomedical devices due to tunable shape memory transition temperature around physiological temperature, steroidal LC units and bioactivity of the building blocks.
10:45 AM - HH7.5
Crystalline and Nanoscale Structure in Shape Memory Hybrid Nanocomposites Determined by Simultaneous WAXS-SAXS Analysis.
Bonifacio Alvarado-Tenorio 1 2 , Angel Romo-Uribe 2 , Patrick Mather 3
1 Posgrado de Ingenieria, Facultad de Quimica, Universidad Nacional Autonoma de Mexico, D. F. Mexico, 2 Instituto de Ciencias Fisicas, Universidad Nacional Autonoma de Mexico, Cuernavaca, Morelos, Mexico, 3 Syracuse Biomaterials Institute, Syracuse University, Syracuse, New York, United States
Show AbstractSimultaneous wide- and small- angle X ray scattering (WAXS-SAXS) has revealed surprisingly highly ordered crystalline and nanoscale structures in polyhedral silsesquioxane-poly-caprolactone (POSS-PCL) nanocomposites. The materials feature a single POSS moiety centered on a PCL chain, yielding two short tethers for a total molecular weight of 2,600 g/mol. WAXS analysis showed for diol-terminated POSS-PCL that both crystalline reflections of the PCL orthorhombic phase and crystalline reflections of POSS rhombohedral phase were present, thus indicating that both crystalline phases coexist. Simultaneously, SAXS revealed two long period spacings: one associated with the POSS nanobuilding blocks (long period of 66 Å), the other a PCL lamellar nanophase (long period of 151 Å). Surprisingly, end-capping of the PCL alcohol groups with acrylate groups (for later network formation) disrupted the rhombohedral crystal lattice of POSS molecules, whereas the orthorhombic phase of PCL remained unchanged. Moreover, SAXS showed only one long period (117 Å) associated with PCL crystalline nanostructure. Thus, the acrylate groups modified the microstructure of the POSS-PCL backbone to a less ordered crystalline and nanostructure form. Networks exhibiting shape memory behavior were obtained by photocuring the acrylate-terminated nanocomposites utilizing a tetrathiol crosslinker, as previously reported[1]. The crosslinked POSS-PCL networks still showed the POSS rhombohedral crystalline phase; however, PCL crystallization was suppressed, resulting in an amorphous PCL phase. Strikingly, SAXS showed that a highly ordered cubic superstructure was present in the crosslinked networks. The cubic superstructure is attributed to clusters formed by POSS molecules. This postulation is supported by the observed POSS crystalline reflections observed by WAXS. The distinct changes in micro and nanostructure upon crosslinking were corroborated by resulting phase behavior observed by differential scanning calorimetry. These investigations of the spatial arrangement at the molecular and nano- scales will be discussed in the context of the observed shape memory effect of the associated networks.[1] K. Lee, P.T. Knight, T. Chung, and P.T. Mather, “Polycaprolactone-POSS Chemical/Physical Double Networks,” Macromolecules 41, 4730-4738 (2008)
11:30 AM - HH7.6
Shape-memory Behavior of Zinc Oleate-filled Elastomeric Ionomers.
Jing Dong 1 , Elise Izzo 2 , R. Weiss 1
1 Polymer Engineering, University of Akron, Akron, Ohio, United States, 2 Polymer Program and Department of Chemical Engineering, University of Connecticut, Storrs, Connecticut, United States
Show AbstractShape memory polymers (SMP) are materials that can change shape when exposed to an external stimulus, such as temperature. SMPs have a permanent shape that is provided by a crosslinked network, but they can be deformed above a critical temperature (Tc) of a second, reversible network and fixed into a temporary shape when cooled under stress to below Tc. When reheated without stress to above Tc, the material reverts to its permanent shape. SMPs have applications in medical devices (e.g., stents and sutures), actuators, sensors, artificial muscles, switches, smart textiles and self-deployable structures. We recently reported that a new type of SMP was successfully prepared using low molecular weight fatty acids or fatty acid salts (FAS) compounded with an elastomeric ionomer, the zinc salt of sulfonated poly{ethylene-r-propylene-r-(5-ethylidene-2-norbornene)}, Zn-SEPDM. The physical crosslinks in the ionomer due to the nanophase separation provided a permanent shape, while the strong intermolecular interactions between the FAS and the Zn-SEPDM formed a thermally reversible, physical network that provided the temporary crosslinks needed for the SMP. The advantage and versatility of this approach is that the Tc of a SMP can be varied over a wide range of temperature, e.g., from 20 to 120 °C, simply by choosing an appropriate fatty acid or salt, while using the same host elastomer. In this talk, we discuss the properties of a series of SMPs prepared from Zn-SEPDM with various amounts of zinc oleate (ZnOl). The thermal properties, mechanical properties, morphologies and the shape memory behavior (shape fixation, shape recovery and the fill factor) were investigated. Zn-SEPDM/ZnOl compounds prepared using Zn-SEPDM with 30 wt% ZnOl exhibited the best fixation, recovery and fill factor. The Tc of the Zn-SEPDM/ZnOl compounds with compositions between 2.5 and 50 wt% ZnOl, varied between 69 ~ 77°C, and the tensile modulus at room temperature ranged from 4.5 to 15 MPa, respectively. Thus, in addition to the ability to vary the properties of the Zn-SEPDM/FAS SMPs over a wide range by changing the FA, the properties of these SMPs are also finely tunable by simply changing the amount of FA used in the compound.(This research was supported by the Polymers Division of the National Science Foundation (Grant DMR 0960461))
11:45 AM - HH7.7
Controlling Bending of Active Gels with Gradients in Cross-link Density.
Olga Kuksenok 1 , Victor Yashin 1 , Ryo Yoshida 2 , Anna Balazs 1
1 Chemical Engineering Dep, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 Department of Materials Engineering , The University of Tokyo, Tokyo Japan
Show AbstractChemo-responsive gels undergoing the Belousov-Zhabotinsky (BZ) reaction exhibit self-sustained pulsations, which can be harnessed to perform mechanical work. To utilize such BZ gels in a number of technological applications, it is critical to develop a robust approach for controlling their bending and stretching. Using our recently developed gel lattice spring model, we focus on the three-dimensional dynamics of chemo-responsive gels that encompass gradients in their cross-link density. Specifically, we simulate the dynamics of long thin rectangular filaments with a gradient in the cross-link density perpendicular to the long axis. We show that the shape of the sample strongly depends on the physical properties of the gel and the parameters of the BZ reaction. We compare our simulation results on the amplitude of bending with respective experimental data. We also simulate the dynamics of BZ gels that contain a helical distribution of the gradient in cross-link density and show that such samples form ``springs'' that exhibit complex motion. Finally, we investigate how bending and spring-like motion of the sample is affected when the sample is attached with one of its ends to a substrate (thus forming an autonomously oscillating cilium). Our studies constitute the first simulation studies of the dynamics of three-dimensional heterogeneous chemo-responsive gels.
12:00 PM - HH7.8
Highly Thermo Responsive Multi-segment Block Copolymer.
Shuhuai Xiang 1 , Deanna Pickel 3 , Jennifer Lu 2
1 School of Natural Science, University of California at Merced, Merced, California, United States, 3 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 School of Engineering, University of California at Merced, Merced, California, United States
Show AbstractAdvancements in sensor, artificial muscle, robot motion, energy conversion and other signal processing related devices require high efficient transducer materials. Polymeric transducer material systems have drawn much attention because of their light weight, easily deformable at low energy input, abundant resources and versatility in designing. Highly thermo responsive multi-segment block copolymers contain polyaromatic amide, rod segments, and polyether, coil segments, has been synthesized using condensation polymerization. Light scattering, GPC, DSC, FTIR and TGA results will be presented to show molecular structures and properties of the block copolymers. Film mechanical properties as a function of crosslink density and volume fraction of rod segment will be discussed. We will present the result demonstrating that the molecular weight of polyether chains can be tuned to response to room temperature heat fluctuation or infrared illumination with fast volume change between melt and solidification processes. Due to physical and chemical properties mismatch, the rod and coil segments are capable of self-assembling into long range ordered structure. By incorporating benzocyclobutane (BCB) moieties and double bonds in the rod segments, thermal crosslinking around 220°C with negligible shrinkage has been achieved for further enhancing mechanical properties. The collective motion of individual thermal switches can be easily observed when exposing a thin polymer film to very low intensity infrared laser (785nm, ~ 20mW/cm2). The thin film shows no fatigue after thousands of response cycles at 1Hz frequency. Combination of the absence of hysteresis with great capability of absorbing and generating strain energy renders this new responsive polymer system with a broad spectrum of applications from microactuator, artificial muscle, thermal sensing to energy conversion devices.
12:15 PM - HH7.9
Thermo-switchable Polymer Dielectrics.
Ross Johnson 1 , Fenil Kholwadwala 1 , Shawn Dirk 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractWe are interested in utilizing the thermo-switchable properties of precursor poly(p-phenylene vinylene) (PPV) polymers to develop capacitor dielectrics that will fail at specific temperatures due to the material irreversibly switching from an insulator to a conducting polymer. By utilizing different leaving groups on the polymer main chain, the temperature at which the polymer transforms into a conductor can be varied over a range of temperatures. Electrical characterization of thin-film capacitors prepared from several precursor PPV polymers indicates that these materials have good dielectric properties until they reach elevated temperatures, at which point conjugation of the polymer backbone effectively disables the device. Here, we present the synthesis, dielectric processing, and electrical characterization of several new thermo-switchable polymer dielectrics.This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000.
12:30 PM - HH7.10
Shape Retention and Learning Effect in Artificial Muscles Based on Conducting Polymer.
Keiichi Kaneto 1 , Kazuo Tominaga 1
1 LSSE, Kyushu Institute of Technology, Kitakushu Japan
Show AbstractMuscles are strengthened by training and show learning effects. How about the conducting polymer artificial muscle? Tensile load dependences of electrochemomechanical strain (ECDS) in artificial muscles based on polyaniline (PANi) films were studied. It was found that conducting polymer artificial muscles show training and learning effects. At large tensile loads >1 MPa, the PANi film showed elongation by creeping of 20-30 %. The elongated state was retained. However, the creeping was recovered by the removable of tensile loads and several electrochemical cycles. The result indicated that the creeping was caused by anisotropic deformation (uniaxial stretching), not slipping and/or breaking of polymer chains. The retention of elongated shape is explained in terms of ionic crosslink by the oxidation, as follows. At oxidized state, conducting polymers are stiff due to the delocalization of pi-electron and ionic crosslink at polaronic species with counter ions. The stiffened state relaxes to soft by electrochemical reduction. During electrochemical processes, the film is softer than those of oxidized and reduced states, since the ions are dynamically flowing, resulting in easy creeping. It was also found that the initial ECMS of 4.8% increased to 6.5% after experience of high tensile loads of 3MPa. The phenomenon can be named as learning or training effect. The learning effect is accounted by the enhanced electrochemical activity. The cyclic voltammogram under tensile loads showed a shift in oxidation and reduction peaks to lower potential, indicating easier oxidation due to shift of HOMO level, resulting from the uniaxial stretching. The ejected or injected charges after removal of tensile loads increased 20-30% compared with those of initial stage, and the ECMS increased in proportion to the charges. The behaviors of ECMS under tensile loads revealed many interesting rheological mechanics and will be given in the talk.
12:45 PM - HH7.11
Manipulating PNIPAAm Microgel Morphology and Thermoresponsive Behavior through Tannic Acid Complexation.
Eunice Costa 1 , Margarida Coelho 1 , Teresa Casimiro 1 , Laura Ilharco 2 , Ana Aguiar-Ricardo 1 , Paula Hammond 3
1 , REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Caparica Portugal, 2 , Centro de Química-Física Molecular, Complexo I, Instituto Superior Técnico, Lisboa Portugal, 3 Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractPoly (N-isopropylacrylamide) (PNIPAAm) is a well known thermoresponsive polymer which has been widely studied for biomedical applications such as biosensing, drug delivery and cell sheet technology. Tannic acid (TA) is a high molecular weight polyphenolic compound with bioprotective activity that has the ability to associate to several synthetic and natural polymers through non-covalent interactions. Herein the complexation of TA onto PNIPAAm microgels was thoroughly investigated for establishing pH-controlled reversible thermoresponsive systems. Cross-linked PNIPAAm particles were initially prepared by free-radical dispersion polymerization in supercritical carbon dioxide (scCO2), rendering pure, well-defined and monodisperse micron-sized spherical beads. The effect of TA concentration and pH on microgels morphology, water uptake and thermoresponsive behavior after TA adsorption was systematically assessed. Moreover, interactions between PNIPAAm and TA were analyzed by diffuse reflectance infrared Fourier transform spectroscopy (DRIFT FT-IR) to elucidate the mechanisms behind the assembled microgels behavior. In fact for PNIPAAm microgels complexed with high amounts of TA (above 5 wt%) the microgels were collapsed and deformed due to strong hydrogen-bonding between PNIPAAm and TA and lost the ability to respond to temperature stimuli. For lower TA weight ratios the microgels exhibited a spherical morphology and its thermoresponsive behavior depended upon assembly pH. At lower pH (pH 4) TA is more protonated and therefore larger TA amounts were adsorbed from the same initial concentration than at higher pH (pH 7), as interactions between TA and PNIPAAm become more favorable with decreasing pH. Furthermore upon titration of non-responsive TA assembled PNIPAAm microgels to a pH above tannic acid pKa (pH 9), hydrogen-bonding between PNIPAAm and TA became weaker and the microgels recovered their thermoresponsive behavior. Moreover tannic acid was still partly retained within the polymeric network, being a quasi-reversible process. These pH controlled thermoresponsive microgels have potential for several applications such as pH on-off switches in microfluidic devices, polyphenol sensors or drug delivery for target areas with mild alkaline pH.
HH8: Thermal and Other Properties and Applications
Session Chairs
Debra Wrobleski
Youlong Xu
Wednesday PM, December 01, 2010
Back Bay B (Sheraton)
2:30 PM - HH8.1
Temperature-responsive Behavior of Dynamically Reconfiguring Polymeric Surfaces and Their Applications.
Philseok Kim 1 2 3 , Jeffrey Epstein 2 , Lauren Zarzar 2 , Baptiste Salley 1 , Sylvain Caron 1 , Joanna Aizenberg 1 2 3
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 2 Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States, 3 Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, Massachusetts, United States
Show AbstractHybrid actuation system combining patterned micro/nanostructures and artificial muscle system that puts these structures in motion is an emerging technology for producing surfaces with dynamically reconfigurable patterns. In particular, when these micro/nanostructures are combined with responsive materials, the system adapts to environmental changes. These dynamic surfaces have potential applications in adaptive optics and photonics, reconfigurable architectures in smart buildings and robotics, generation of flow and propulsion of particulate matter, anti-fouling and anti-bacterial surfaces. We have recently developed such adaptive and dynamic systems based on polymeric microbristle embedded in a humidity-responsive hydrogel that can be reversibly actuated upon hydration and drying. Here we have further developed this system to be responsive to other stimuli such as pH, temperature, and electric field. Particularly, we will present temperature-responsive dynamic systems and their applications for adaptive temperature control. Microplatelet arrays were embedded in temperature-responsive hydrogels such as poly(N-isopropyl acrylamide) with precisely tuned lowest critical solution temperature (LCST). The surface of each microplatelet was selectively coated with a reflective material (e.g. metallic coating) making each plate acting as a microreflector. We will present how these temperature-responsive hybrid polymer actuators adaptively control the light transmission and behave as a thermal insulation when used as a screen.
2:45 PM - HH8.2
Sharp Lower Critical Solution Temperature Transition for Novel N-isopropylacrylamide Based Polymer.
Mahriah Alf 1 , T. Alan Hatton 1 , Karen Gleason 1
1 Chemical Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractA novel, thermally responsive N-isopropylacrylamide (NIPAAm) based polymer with a sharp lower critical solution temperature (LCST) for conformal and substrate independent surface modification is presented. Initiated chemical vapor depositon (iCVD) is a solventless, gentle, one-step process used here to deposit thin films of the lightly cross-linked polymer, poly(N-isopropylacrylamide-co-di(ethylene glycol) divinyl ether) (p(NIPAAm-co-DEGDVE)). The polymer’s bulk responsive characteristics are investigated using quartz crystal microbalance with dissipation monitoring (QCM-D), showing a sharp LCST transition curve with inflection point at 28.5 ± 0.3 °C. Static contact angle measurements explore the surface responsive properties on both flat and nanostructured surfaces. The change in contact angle around the LCST increases from 30° on a flat surface to 85° on a conformally coated forest of multi-walled carbon nanotubes (MWCNTs). A range of cross-linker densities is explored as well to understand how the volumetric and surface responsive characteristics.
3:00 PM - HH8.3
A Thermodynamic Model of Physical Gels.
Hanqing Jiang 1 , Yonghao An 1 , Francisco Solis 1
1 , Arizona State University, Tempe, Arizona, United States
Show AbstractPolymeric gels are materials where linear polymer segments are joined at crosslinking points to form a three-dimensional network. The nature of the cross-links determines central characteristics of the polymeric gels. Physical gels are characterized by dynamic cross-links that are constantly created and broken. The environmental factors (e.g., temperature) affect the bonding strength of the cross-links and in turn change the states of physical gels from solid to liquid. The restructuring ability of physical gels makes them an important class of materials with many applications, such as in drug delivery. We present a thermodynamic model for physical gels that considers both the elastic properties of the network and the transient nature of the cross-links. The cross-links’ reformation is captured through a connectivity tensor M at the microscopic level. The macroscopic quantities, such as the volume fraction of the monomer, number of monomers per cross-link s, and the number of cross-links per volume q, are defined by statistic averaging. A variational mean-field energy functional for the gel is constructed. The equilibrium equations and the stress are obtained at the current state. We discuss the static thermodynamic properties predicted by the model. The problems of un-constrained swelling and stress driven phase transitions of physical gels are studied and then we describe the conditions in which these phenomena arise as functions of the bond activation energy Ea, polymer/solvent interaction parameter chi, and external stress p.
3:15 PM - HH8.4
Electrochemically Triggered Dissolution and Swelling of Layer-by-layer Polymer Thin Films.
Daniel Schmidt 1 , Younjin Min 1 , Paula Hammond 1
1 Chemical Engineering Department, MIT, Cambridge, Massachusetts, United States
Show AbstractElectroresponsive polymer thin films hold promise for a number of applications including drug delivery, separations, mechanical actuation, and dynamic adhesion, friction, and damping, among others. Here we generate layer-by-layer self-assembled thin films that are used to coat electrodes, and utilize the electrochemical reduction of dissolved oxygen to raise the local pH at the electrode-film interface while maintaining a near constant bulk pH. We focus on two previously reported, pH-responsive polymer systems. The first system comprises polyvinylpyrrolidone and tannic acid self-assembled based on hydrogen-bonding interactions. In general it requires a bulk pH greater than 8.75 to induce dissolution of these films, while here we show that application of potentials ranging from -0.25 V to -1.00 V (vs. SCE) induces rapid (30 sec to 8 min) dissolution of 150 nm thick films at a bulk pH of ~5.5. We found that the rate of dissolution depends upon both the magnitude of the applied voltage and the concentration of dissolved oxygen. The second system of interest comprises polyallylamine hydrochloride and poly(4-styrene sulfonate) self-assembled based on electrostatic interactions. It has been shown that these films undergo a superswelling transition (400-800% degree of swelling) below pH 4, and can be deswollen to the original film thickness at pH >10.5. Here, we show that the dramatic deswelling transition may be triggered by application of the same relatively low electric potentials mentioned above at a bulk pH of 3-4, thus yielding significant changes in surface properties. Through the two systems described above, we show the power of an electrochemical stimulus to induce drastic changes in certain “smart” polymer thin films. We maintain that utilization of electrochemically induced local pH changes as an alternative to large bulk pH changes makes pH-responsive polymer thin films more versatile and more promising for biomedical applications in particular.
3:30 PM - HH8.5
Redox-responsive Polymeric Materials for CO2 Capture.
Renu Ravindranath 1 , Fritz Simeon 1 , Howard Herzog 2 , Alan Hatton 1
1 Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 MIT Energy Initiative, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractGlobal warming resulting from contributions of gases generated by human activities has been discussed for several years. Recently, the part played by increased atmospheric CO2 has received much attention and Carbon Capture and Storage (CCS) is the potential method for mitigating carbon dioxide (CO2) emissions in the atmosphere. Current commercial CO2 capture technology based on alkanolamines is expensive and energy intensive. Developing new and economic CO2 capture processes particularly in clean coal technology is in the forefront of recent sustainable energy research. Four major methods are developed for CO2 separation and capture; (i) solution absorption, (ii) adsorption, (iii) membrane diffusion, and (iv) cryogenic. Among them, adsorption is of great interest due to its low energy consumption, low equipment cost, and easiness to be applied. A range of materials have been employed for CO2 adsorption. However, the low CO2 selectivity of the adsorbents limited the application of this method. The present study describes the development of redox responsive polymeric materials for electrochemically driven chemisorption as an alternative for CO2 capture which has the potential for an energy efficient system. We have designed and developed redox responsive conjugated polymeric materials containing CO2 capturing moieties. Towards this a series of polymers were synthesized and evaluated its electrochemical response towards CO2 capture using cyclic voltammetry. The high surface area polymeric films were tested as solid sorbent for the electrochemically driven capture of CO2. The present talk will be focused on the design and development of electrochemically responsive polymeric films for CO2 capture.
3:45 PM - HH8.6
pH-Responsive Actuation of Polymeric Microstructures in Fluid.
Lauren Zarzar 1 , Philseok Kim 2 3 , Joanna Aizenberg 1 2 3
1 Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States, 2 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 3 Wyss Institute for Biologically Inspired Engineering, Harvard University, Cambridge, Massachusetts, United States
Show AbstractResponsive actuation on the microscale is of interest for applications ranging from MEMS to biofilm prevention to microfluidics and propulsion. We build upon our previous work on humidity-responsive actuation of high-aspect-ratio polymeric structures and alter the system to be sensitive to pH by using an acrylic acid-co-acrylamide hydrogel with a volume transition at pH=4.2. Actuating surfaces remain submerged making them more ideal for fluidic applications such as propulsion, microfluidic networks and mixing. We also observe and describe unusual non-linear waves created in the surface-attached hydrogels that experience dynamic creasing upon swelling which exerts anisotropic forces on the embedded microstructures resulting in patterned micropost deflections. Polymeric actuators embedded in the pH-responsive hydrogel can be patterned within microfluidic channels by non-conventional methods and put in motion by flow of acid and base, or by reversible electrochemically generated pH gradients. By utilizing laminar flow of acid and base in microchannels coated with microplates embedded in pH-responsive gel, we can induce controllable reversible bending and actuation of microstructures and unique flow patterns in microchannels.
4:30 PM - HH8.7
Using Porphyrin Emission to Monitor Membrane Stability.
Neha Kamat 1 , Zhengzheng Liao 2 , P. Ghoroghchian 4 , Michael Therien 3 , Ivan Dmochowski 2 , Daniel Hammer 1
1 Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 4 Medicine, Brigham and Women's Hospital, Boston, Massachusetts, United States, 3 Chemistry, Duke University, Durham, North Carolina, United States
Show AbstractMolecular rotors, fluorescent molecules that exhibit environment-dependent fluorescence lifetimes and intensities, are showing promise as solvent, fluid flow, and viscosity sensors in biological environments. Conjugated porphyrin molecules have proved useful in this regard since the twisting of the various subunits of the dye can lead to appreciable shifts in the peak emission wavelength. The emission wavelength of the dye can in turn be used to obtain information about the dye environment. A family of near infra-red fluorophores, which consist of highly conjugated ethyne-bridged oligo(porphinato)zinc(II) molecules (PZn n), have previously been synthesized and their interactions with polymer chains in bilayered nanoscale vesicular environments have been studied. The hydrophobic nature of these porphyrins allow them to be encapsulated into vesicle membranes made by diblock-copolymers (polymersomes), and in the current study, we show the dye can be encapsulated into cellular membranes as well. A series of porphyrin molecules were encapsulated into polymersome membranes and demonstrated environment-sensitive emission shifts upon changes in porphyrin loading, identity of the polymer make-up of the membrane, type of porphyrin, and membrane stability. Porphyrin loading was increased in polymersome membranes from 0.1 to 40 mol % and the resulting peak-emission red shifted by approximately 30 nm for the dyes tested. The red shift in emission indicates a porphyrin population shift from a twisted conformation to a more planar conformation as dye loading was increased in the membrane and further suggests that a loss of conformational freedom forces the dyes into a planar state. This emission red shift was reduced when the vesicle membrane area was increased by using a larger molecular weight diblock copolymer. The emission of the porphyrin dyes were then used to study vesicle-membrane stability. In both photo-active polymersomes (that rupture in response to light) and in polymersomes lysed with detergents, porphyrin emission was found to shift in response to changing membrane stability. Porphyrin emission shifts were also studied in vesicles made from the biodegradable polymer poly(ethyleneoxide)-block-poly(ε-caprolactone) (PEO-b-PCL). We hypothesize that the NIR emission of these porphyrin dyes can be used to monitor release and delivery of drugs from polymersomes in cells. A potential use of membrane-loaded porphyrins is to elucidate areas of membrane stress or stretching, where loss of conformational freedom of the porphyrin may causes a shift in its emission.
4:45 PM - HH8.8
Chemically Actuated Microgrippers Based on Polymeric Triggers.
Jatinder Randhawa 1 , Timothy Leong 1 , Noy Bassik 1 , Michael Keung 1 , Evin Gultepe 1 , David Gracias 1
1 Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractA dominant paradigm in engineering is to fabricate microsystems that are triggered by electrical, thermal, or pneumatic signals. We describe the utilization of polymeric triggers to control actuation of microtools such as grippers based on a chemical cue. Actuation is triggered when a mechanical property change is induced in the polymer as a result of swelling, dissolution, delamination or chain-scission. Hence we were able to construct grippers that could be actuated on exposure to chemicals. Additionally, the inclusion of ferromagnetic components within the grippers allowed us to move them from distances as far away as several centimeters. We will discuss the use of several polymers; the right choice of polymer and exposed chemical controls the response time as well as the curvature of bending of specific hinges and hence response of the microtool. We will also discuss specific applications such as picking objects [1], and biopsy-like [2] procedures. These polymer trigger based microsystems are a convenient strategy to enable the creation of Micro Chemo-Mechanical Systems (MCMS) that are actuated by chemistry as opposed to electricity [as in Micro Electro-Mechanical Systems (MEMS)].[1] J. S. Randhawa, T. G. Leong, N. Bassik, B. R. Benson, M. T. Jochmans and D. H. Gracias, “Pick-and-Place using Chemically Actuated Microgrippers”, Journal of the American Chemical Society (JACS) 130, 17238 (2008). [2] T. G. Leong, C. L. Randall, B. R. Benson, N. Bassik, G. M. Stern and D. H. Gracias, Proceedings of the National Academy of Sciences (PNAS) 106, 703-708 (2009).
5:00 PM - HH8.9
Novel Synthetic Route for Smart Stimuli-responsive ``Janus” Organic/Inorganic Hybrid Particles.
Young Kuk Jhon 1 2 , Douglas Kiserow 1 2 , Jan Genzer 2
1 Chemical Sciences, Army Research Office, RTP, North Carolina, United States, 2 Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractControlled fabrication of hybrid organic/inorganic materials has made a great impact on many novel structures and devices, including, optoelectronic materials, templates for metal deposition and replica molding, masks for photolithography, bio-compatible inorganic materials, drug delivery, biosensing, and separation of biomaterials, to name a few. Various approaches have been developed that attempt to make particles covered with a tethered polymer brush on one side to provide bridge between organic compounds (i.e. polymers) and non-organic materials (e.g. silicon oxide, gold, silver, aluminum oxide, and ferro oxide). One of the promising routes for forming the hybrid material involves fabrication of asymmetrically functionalized particles known as “Janus” particles. We will present a novel synthetic route for forming organic/inorganic hybrid particles by growing polymer brushes using surface-initiated atom transfer radical polymerization (SI-ATRP). First, a monolayer of spherical silica particles was cast on flat silicon wafers or glass slides using “convective assembly”. Subsequently, the upper portions of the particles in the monolayers at the free surface were exposed to organosilane vapor with three functional groups, amine (−NH2), methyl (−CH3), and trifluoromethyl (−CF3), which formed organized monolayers. After removing the particles from the substrate, the unmodified hemispheres were coated with organosilane-based initiators, which served as active centers for SI-ATRP of thermoresponsive (poly(N-isopropylacrylamide) (pNIPAM) brushes. This produced “Tailed Janus Particles” (TJP) that may be useful building blocks due to the structural asymmetry (polymer vs. functional monolayer) and the thermoresponsive properties (tailoring the thickness and hydrophobicity of the polymeric grafts).
5:15 PM - HH8.10
Polymer Membrane Patterning for Sensor Applications.
Maria Dinescu 1 , Alexandra Palla-Papavlu 1 , Valentina Dinca 1 , Domenico Cannata 2 , Fabio Dipietrantonio 2 , Massimiliano Benetti 2 , Enrico Verona 2 , Thomas Mattle 3 , James Shaw-Stewart 3 4 , Thomas Lippert 4
1 , NILPRP, Bucharest Romania, 2 , "O.M.Corbino" Insitute of Acoustics, Rome Italy, 3 General Energy Research Department, Paul Scherrer Institute, Villigen Switzerland, 4 Laboratory for Functional Polymers, EMPA, Swiss Federal Laboratories for Materials Testing and Research, Dübendorf Switzerland
Show AbstractIncreased selectivity, response speed, and sensitivity in the chemical and biological determinations of gases and liquids are of great interest. Herein we describe new opportunities in the research of polymer sensor materials that have been opened up through the use of laser based methods. We show that polymeric sensor materials i.e. polyepichlorhydrine (PECH), polyisobutylene (PIB) and polyethyleneimine (PEI) are applicable to SAW type sensors because of their extremely broad range of capabilities. In this work polymer pixels are printed on chemoselective sensor structures by laser induced forward transfer (LIFT). To avoid direct interaction of the laser with the “soft” polymeric materials a triazene polymer (TP) which acts as a Dynamic Release Layer (DRL) is used. A parametric study (i.e. laser fluence, donor film morphology and thickness as well as single versus multiple pixel deposition) was carried out to determine the optimum experimental conditions under which sensitive polymer pixels are obtained. Following the morphological and structural characterization, the responses of the polymer coated sensors were measured and it was found that only in a narrow range of laser fluences the interdigital transducers (IDT) of the sensor devices are not damaged. In addition, single pixels are preferable to multiple polymer pixels and the thickness of the polymer to be printed shouldn’t be higher than the thickness of the DRL layer. Furthermore, the sensitivity of the polymer coated devices to different analyte concentrations gives an indication that LIFT can be used for printing sensitive polymer pixels onto sensor devices.Keywords: LIFT, PIB, PEI, PECH, SAW
5:30 PM - HH8.11
Poly(vinylidene fluoride-trifluoroethylene) (72/28)(%mol) Interconnected Porous Membranes Obtained by Crystallization from Solution.
Armando Ferreira 1 , Jaime Silva 1 2 , Vitor Sencadas 1 , Jose Luis Gomez-Ribelles 3 4 5 , Senentxu Lanceros-Mendez 1
1 , Departamento de Fisica da Universidade do Minho, Campus de Gualtar, 4710-057, Braga Portugal, 2 , IPC-Institute for Polymers and Composites, University of Minho, Campus de Azurem, 4800-058, Guimarães Portugal, 3 , Centro de Biomateriales, Universidad Politécnica de Valencia, 46022, Valencia Spain, 4 , Regenerative Medicine Unit, Centro de Investigación Príncipe Felipe, Autopista del Saler 16, 46013 Valencia , Valencia Spain, 5 , 5CIBER en Bioingeniería, Biomateriales y Nanomedicina, Valencia Spain
Show AbstractPorous materials find a number of technological applications. In particular, fabrication of porous membranes made of poly(vinylidene fluoride), PVDF, and PVDF copolymers have attracted technological interest due to the potential applications as filters, as it remains inert to many harsh chemicals due to its chemical resistance [1]; as polymer electrolyte for applications in rechargeable batteries [2]; and in biomedical applications [3]. Electroactive macroporous poly(vinylidene fluoride-trifuoroethylene), P(VDF-TrFE) (72/28), membranes with a well organized porous structure and thickness from 30 to 250 µm have been produced by solvent evaporation at room temperature starting with a diluted solution of the co-polymer in dimethylformamide. The pore architecture consists of spherical interconnected pores, pore walls being formed by adhered spherical polymer crystals. The pore size can be up to an average pore size of 20 µm, depending on the initial solvent/polymer relative concentration. Thinner 1 and 2 µm thick membranes prepared by spin coating also show a similar microstructure provided the concentration of the initial solution is high enough. This microstructure has been explained by a liquid-liquid spinodal decomposition followed by polymer crystallization [4]. The polymer phase is in the electroactive phase of the polymer, showing therefore piezoelectric and pyroelectric effects.Acknowledgements The authors thank the Portuguese FCT (Grants PTDC/CTM/73030/2006, PTDC/CTM/69316/2006 and NANO/NMed-SD/0156/2007 and SFRH/BPD/63148/2009 (V.S.)) and the Spanish Ministry of Education and Ministry of Science and Innovation (Project No. MAT2007-66759-C03-01). References[1] HS Nalwa, in Ferroelectric Polymers: Chemistry, Physics, and Applications, Vol 1, Marcel Dekker Inc, New York 1995.[2] Q Xiao, X Wang, W Li, Z Li, T Zhang, H. Zhang., J Membr Sci 2009, 334, 117.[3] U Klinge, B Klosterhalfen, AP Öttinger, K Junge, V Schumpelick, Biomaterials 2002, 23, 3487.[4] A. Ferreira, J. Silva, V. Sencadas, J.L. Gómez Ribelles and S. Lanceros-Méndez, Macromolecular Materials and Engineering, DOI: 10.1002/mame.201000020, 2010
5:45 PM - HH8.12
High Speed and Reproducibility of Ultrathin Polymer Field-effect Transistors by Direct Pen Painting Method.
Yasuhiko Hayashi 1 , J. Nishikawa 1 , K. Hayashi 1 , T. Nagaya 1 , K. Nakamura 2 , T. Takigawa 2
1 Department of Frontier Materials, Nagoya Institute of Technology, Nagoya, Aichi, Japan, 2 Research Laboratories, DENSO CORPORATION, Nisshin, Aichi, Japan
Show Abstract The performance of organic thin film transistors (OTFTs) based on conjugated polymers has improved greatly in recent years and received considerable attention because it can be fabricated at low temperature and potentially reduced cost compare to traditional silicon-based TFTs. We have developed a low-cost, high-throughput Direct Pen Painting (DPP) method that uses a pen tip, like a white board maker, to deliver polymer to a patterned substrate surface in a “direct paint” manner. Among a wide variety of processing methods, DPP allows to control the average orientation and the azimuthal molecular alignment of polymer to improve performances of polymer OTFTs. The source and drain electrodes were patterned and deposited Au/Cr. The poly(3-hexylthiophene) (P3HT) was dissolved in dichlorobenzene and filled it inside the ink cartridge. The surface of SiO2 was treated with octadecyltrichlorosilane (ODTS). The painting speed and pressure of the pen were mainly varied in the experiments in the air. The average mobility and the on/off ratio of TFTs fabricated by painting across the channel are about 40 times higher and 10 times higher than those of TFTs fabricated by painting along with the channel, respectively. The threshold voltage of TFTs fabricated by painting across the channel is about -5 V. It is found that the thickness of films showed extremely thin below 5 nm. Based on results, it is necessary to reduce the film thickness below 10 nm to obtain high performance of P3HT OTFTs. The polymer backbones are orientated along the painting direction confirmed by grazing-incidence X-ray-diffraction measurements using a synchrotron X-ray beam. DPP solution-process is an effective method to fabricate the well-controlled molecular alignment of the P3HT film and its OTFTs. The observed improvements of OTFTs due to painting direction may be because of fewer barriers to neighboring molecules which have to be overcome. The high-reproducibility OTFTs based on the P3HT film exhibits high-performance of mobility up to 0.43 cm2/Vs and the on/off ration of 107, which is much higher than the best values of 0.3 cm2/Vs and 104 reported by A. J. Heeger et al., using dip coat method. We also apply the DPP method to high carrier mobility of poly(2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophenes) (pBTTT). The DPP of functional electronic materials may provide a new route to low-cost fabrication of integrated polymer circuits.
Symposium Organizers
Zhongyang Cheng Auburn University
Vivek Bharti 3M Company
Zhuo Xu Xi’an Jiaotong University
Debra A. Wrobleski Los Alamos National Laboratory
HH9: Fabrication / Process and Nanofiber
Session Chairs
Dawnielle Farrar
Huaxiang Yang
Thursday AM, December 02, 2010
Back Bay B (Sheraton)
9:30 AM - HH9.1
Poly(γ-benzyl α,L glutamic acid) – Based Piezoelectric Films and Microfibers.
Dawnielle Farrar 1 2 3 , James West 3 4 , Wonkyu Moon 5 , Michael Yu 2
1 , Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, United States, 2 Materials Science & Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 3 Electrical & Computer Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 4 Mechanical Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 5 , Pohang University of Science & Technology, Pohang Korea (the Democratic People's Republic of)
Show AbstractHere, we present new composite films and microfibers based on the biopolymer, poly(γ-benzyl α,L-glutamate) (PBLG) and discuss their fabrication and piezoelectric properties. Fabrication of PBLG films and fibers was made possible by PBLG’s extreme solubility in organic solvents. By simultaneous poling and curing of PBLG/methylmethacrylate (MMA) mixture solutions via corona charging, we fabricated a flexible composite film [80% PBLG and 20% Poly(methylmethacrylate) (PMMA)] with approximately 20% of the PBLG molecules oriented normal to the film surface. This PBLG film exhibited high piezoelectricity (d33 = 20 pC/N), and its Young’s modulus was 1 GPa. In an effort to optimize net dipole orientation in PBLG, we produced piezoelectric microfibers (diameter: 100 nm) with nearly all of the PBLG dipoles oriented along the fiber axis, evidenced by x-ray diffraction. The PBLG fibers showed high piezoelectricity (d33 = 32 pC/N), and an elastic modulus of 570 MPa. Both the piezoelectric film and fiber systems can be fabricated directly from solution in a mould or on a substrate. Due to the versatility in the fabrication process and the high piezoelectricity, these materials show great promise as transducer materials for loud speakers, microphones, and/or energy harvesting devices.
9:45 AM - HH9.2
Stimuli Responsive Coaxial Polymer Nanotubes.
Gozde Ozaydin-Ince 1 2 , Karen Gleason 1 , Melik Demirel 1 3
1 Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Faculty of Engineering and Natural Sciences, Sabanci University, Istanbul Turkey, 3 Materials Research Institute and Department of Engineering Science, Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractHigh aspect ratio polymeric nanotubes of stimuli responsive polymers are fabricated using initiated chemical vapor deposition (iCVD). Using vapor deposition techniques, challenges of solution phase deposition techniques, such as control of the wall thickness or deposition of crosslinked polymers can be overcome. In this work, we report fabrication of highly swellable, well-ordered arrays of hydrogel nanotubes. Degree of swelling and the amount of protein adsorption are controlled by varying the crosslinking density of the nanotubes. Good control of the wall thickness achieved by iCVD, also enables to deposit coaxial nanotubes of different stimuli responsive polymers. Coaxial nanotubes of hydrogel and shape memory polymers are fabricated using AAO templates. The stimuli response of these coaxial nanotubes is studied through the burst release of a model fluorescent molecule.
10:00 AM - HH9.3
Self-Doped Carboxylated Polyaniline Nanofibres.
Larisa Florea 1 , Emer Lahiff 1 , Dermot Diamond 1
1 CLARITY: The Centre for Sensor Web Technologies, Dublin City University, Dublin Ireland
Show AbstractPolyaniline (PAni) is an example of a conducting polymer whose properties (optical/electrical) change in response to changes in the immediate environment of the material. PAni thus has huge potential for sensing applications. By focusing on PAni nanofibres we can dramatically increase the surface area of the material [1]. Our focus is to explore the self-doping behavior of carboxylic acid functionalised PAni nanofibres. The covalent attachment of carboxylic terminated side-chains is achieved by post-polymerisation reflux in the presence of a nucleophile. Using the technique described, control over the extent of functionalisation can be achieved [2,3], while simultaneously maintaining the intrinsic nano-morphology of the polymer material.We provide evidence that although the functionalised PAni is doped with the proton of strong acids at low pH via protonation of amines, at pH greater than 4 when the covalently attached carboxylic acid groups begin to ionize, due to their proximity and the high local concentration of carboxylic acids groups in the vicinity of the nitrogen in the polyaniline backbone, carboxylic acid functions as the dominant dopant thus making this material self-doping. Carboxylic acid functionalised polyaniline shows electroactivity and conductivity even in neutral to basic pHs, thus proving that using the technique described the stability of the material can be improved.The resulting material is characterised using electron microscopy, thermal gravimetric analysis and a range of spectroscopic techniques. The techniques used confirm both the covalent attachment of functional side-groups to the surface of PAni nanostructures, and also reveal the material to be self-doping. While these functionalised PAni nanofibres materials are themselves inherently interesting, they are also attractive as molecular scaffolds for building more complex derivatives that retain the nanostructure and characteristics of PAni [4], while introducing additional functionality such as improved selectivity. A self-doped polyaniline modified electrode has been developed indicating a good electrochemical activity in a wide pH range and showing electrocatalytic activity for the oxidation of ascorbic acid even in neutral PBS solutions.[1] J.X Huang, S. Virji, B.H. Weiller, R.B. Kaner, J.Am.Chem.Soc.125 (2003), 314-315.[2] E.Lahiff, T. Woods, W. Blau, G.G. Wallace, D. Diamond, Synth. Met. 159 (2009), 741-748.[3] E. Lahiff, S. Scarmagnani, B. Schazmann, A. Cafolla, D. Diamond, International Journal of Nanomanufacturing, Vol. 5, (2010). [4] E. Lahiff, S. Bell, D. Diamond, Mater. Res. Soc. Symp. Proc. 1054 (2008), 1054-FF05-05.
10:15 AM - HH9.4
Polyethylene Nanofibers with Very High Thermal Conductivities.
Sheng Shen 1 , Jonathan Tong 1 , Ruiting Zheng 1 , Gang Chen 1
1 Mechanical Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractUltradrawn polyethylene nanofibers are demonstrated to have thermal conductivities as high as ~ 100 W/m.K along the fiber direction, which is comparable to many metals and is 3 orders of magnitude larger than the typical thermal conductivity of bulk polymers. The high thermal conductivity is attributed to the restructure of polymer chains in nanofibers by stretching, which improves the fiber quality toward the "ideal" single crystalline fibers. Our results suggest that high thermal conductivity polyethylene nanofibers may be able to serve as a cheaper alternative to conventional metal-based heat transfer materials in a wide range of applications.
10:45 AM - HH9.5
Temperature Adaptive Insulation Based on Multi-component Fibers of Various Cross-sections.
Barry DeCristofano 1 , Stephen Fossey 1 , Elizabeth Welsh 1 , Jeffrey Perry 1 , Deana Archambault 1
1 , US Army Natick RD&E Center, Natick, Massachusetts, United States
Show AbstractWe have developed a thermal insulation based on bi-component fibers that adapts to its thermal environment, providing greater insulation at low temperatures than at warmer temperatures. The analysis of bi-metallic strips done by Timoshenko for strips of rectangular cross-section concluded that “…curvature is proportional to the difference in elongation of the two metals and inversely proportional to the thickness of the strip.” We have extended Timoshenko’s formulation and applied it to bi-component fibers of circular and triangular cross-sections. In each case, the curvature resulting from the balance of the axial forces and bending moments has been brought into a standard form inversely proportional to (A+Bn+C/n) where n is the ratio of the moduli and A, B, and C are functions of the geometry of the two components. An important consequence of this result is that for any “n” there is a maximum curvature where (A+Bn+C/n) is a minimum. We have used the process of melt-spinning to produce fibers with circular and triangular cross-sections, varying the proportion of the two components. The polymers used have widely different coefficients of thermal expansion. These fibers spontaneously form mats at room temperatures. The experimentally measured thickness changes are in good agreement with the analytical results for fiber bending. The most effective samples to date change thickness by more than 1.5% per degree C (30% over a temperature range from approximately 20°C to 0°C).
11:00 AM - HH9.6
Mechanical and Electrical Properties of a Hybrid Material for Micro-actuation Applications.
Beatriz Lopez-Walle 1 2 , Antonio Elizondo-Martinez 1 2 , Mayra Llamas-Hernandez 1 2 , Carlos Gutierrez-Duran 1 2 , Edgar Reyes-Melo 1 2
1 División de Estudios de Posgrado, FIME, Universidad Autónoma de Nuevo León, San Nicolás de los Garza, Nuevo León, Mexico, 2 CIIDIT, Universidad Autónoma de Nuevo León, Apodaca, Nuevo León, Mexico
Show AbstractA new hybrid material consisting of nanoparticles of iron oxide embedded in carboximetilcellulose and reacting to external magnetic fields has been applied as an electromagnetic micro-actuator. In order to optimize it, mechanical and electrical properties of the hybrid material are presented in this work. First, the deformation of the hybrid material against a variable magnetic field is evaluated. Then, some experimental voltage-current tests are carried out to elucidate electrical phenomena closely related to the performance of the hybrid material working as a micro-actuator. Results show that the maximal deformation observed of a beam-shaped structure (17 x 3 x 0.3 mm3) is 2 mm and depends on many factors (geometry, position, dispersion of the nanoparticles, etc.). In addition, the principal mechanism of electrical conduction is obtained by dipolar orientation.
11:15 AM - HH9.7
`Designer' Biomaterials via Electrohydrodynamic Co-jetting.
Srijanani Bhaskar 1 , Nicholas Clay 2 , Kelly Pollock 4 2 , Joerg Lahann 1 2 3
1 Macromolecular Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Chemical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 4 Chemical Engineering, Cornell University, Thaca, New York, United States, 3 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractControl over nano- and microscale architecture of polymeric materials is highly desirable for improved versatility, utility, and performance of biomedical devices, which include smart drug release systems, biomedical coatings, surgical dressings, and multiplexed bioassays. Apart from size and shape of polymeric micro-objects, phase distribution, or selective material compartmentalization has been shown to be increasingly important for maximizing device performance. The fabrication of multicompartmental microparticles and microfibers from polymer solutions via electrohydrodynamic co-jetting is herein demonstrated.2 In its simplest form, two polymer solutions are flown through a modified side-by-side capillary system. Application of an electric field results in the formation of an electrified jet, and solvent evaporation results in particle formation. The interface between two polymer solutions is sustained during jet fragmentation and size reduction. Because of its intrinsic simplicity and generality, the electrohydrodynamic co-jetting process can be applied to a wide range of specialty and non-specialty materials such as polylactides, polyethyleneimine, polymethyl methacrylate. Furthermore, simple variations of different solution and process parameters, such as concentration, flow rate, applied voltage, etc. provides access to a vast repertoire of shapes and sizes of particles. Such novel particle geometries enable independent control of key parameters, such as chemical composition, surface functionalization, biological loading, shape, and size for each compartment. In this work, we demonstrate the fabrication of multicompartmental particles and fibers from biodegradable polylactide polymers via electrohydrodynamic co-jetting. We then demonstrate the versatility of this process by fabricating a variety of non-equilibrium biphasic shapes, such as discs and rods, in addition to spheres. Spatioselective control over particles’ surface is demonstrated via introduction of free acetylene groups in one hemisphere of biphasic microparticles, and its selective surface modification via “click chemistry”. We then combine this selective surface functionalization with biotin-streptavidin interactions to show orientation and assembly of bicompartmental particles on surfaces modified via chemical vapor deposition. The optical effects achieved through this specific orientation can be employed as diagnostic markers and have applications in developing analyte specific biological assays. Furthermore, by incorporation of polyethyleneimine into biphasic particles, we also demonstrate selective swelling, degradation and controlled release of siRNA.
11:30 AM - HH9.8
Development of a Dual Growth Factor Loaded Biodegradable Hydrogel and Its Evaluation on Osteoblast Differentiation in vitro.
Deepti Dyondi 1 2 , Thomas Webster 2 , Rinti Banerjee 1
1 Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India, 2 Division of Engineering, Brown University, Providence, Rhode Island, United States
Show AbstractHydrogels with their tunable properties are attractive candidates for developing tissue engineering scaffolds for various applications including bone and cartilage. The current work involved studying the synergistic effect of basic FGF and PDGF-BB entrapped within injectable porous gels for bone regeneration applications. An in situ gelling system was developed using bacterial polysaccharides- gellan gum and xanthan gum by temperature and ionic gelation using Ca+2. The hydrogel was characterized and optimized for gelling times such that the gel mixture remains a low viscosity liquid at room temperature but forms a highly viscous gel upon injection at the injury site within a few minutes fast enough for any leakage to be prevented. After characterizing the hydrogels, a dual growth factor release system was developed wherein growth factors- PDGF-BB and basic FGF, were encapsulated within chitosan nanoparticles embedded in the gels as well as directly within the gel. A highly porous hydrogel structure was observed by SEM and TEM studies which showed a slow and sustained growth factor release from the gel system. The use of nanoparticles for encapsulating growth factor within the porous gel matrix further improved the bioavailability of growth factors within the defect site by exhibiting a slow drug release profile as was observed with the in vitro growth factor release studies in PBS (pH 7.4, 37°C) (49% cumulative release for basic FGF from nanoparticles in gel matrix by day 21). Human fetal osteoblasts (CRL 11372) were entrapped within hydrogel prepared from gellan and xanthan gums and a 21-day osteoblast differentiation study was conducted. The hydrogel with its entrapped growth factors showed improved total protein synthesis as well as increased collagen content by day 21. Further evaluation regarding mechanical properties and expression of osteogenic differentiation marker genes are ongoing.
11:45 AM - HH9.9
Polyelectrolyte Adsorption on Microstructured Titanium Surface to Increase Wettability.
Jung Hwa Park 1 , Zvi Schwartz 2 , Rene Olivares-Navarrete 2 , Barbara Boyan 2 , Rina Tannenbaum 1 3
1 School of Materials Science and Engineering, Georgia Tech, Atlanta, Georgia, United States, 2 Biomedical Engineering, Georgia Tech, Atlanta, Georgia, United States, 3 Chemical Engineering, Technion-Israel Institute of Technology, Haifa Israel
Show AbstractMicron-scale and submicron-scale surface roughness enhances osteoblast differentiation on titanium (Ti) substrates in vitro and increases bone-to-implant contact in vivo. However, the low surface wettability as a result of increased surface roughness can delay initial interactions with the physiological environment. Coating surfaces with polyelectrolytes is a versatile approach to develop a robust and conformal surface through electrostatic forces. We examined polyelectrolyte adsorption on titanium surfaces with micron-scale and submicron-scale roughness (PT, Ra ≤ 0.3 µm and SLA, Ra > 3.0 µm) using chitosan (CHI), poly(L-glutamic acid) (PGA), and poly(L-lysine) (PLL). Surface characterization was performed with X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), contact mode profilometry, and contact angle measurements. High resolution XPS spectra indicated that polyelectrolytes indeed adsorbed on PT and SLA surfaces. The surface coverage of the polyelectrolyte adsorbed on Ti surfaces was evaluated with the pertinent SEM images and XPS peak intensity as a function of polyelectrolyte adsorption time on Ti surface. PLL was coated in a uniform thin layer on the PT surface. CHI and PGA were coated evenly on PT, albeit in an incomplete monolayer. CHI, PGA, and PLL were coated on SLA surface with complete coverage. The selected polyelectrolytes increase surface wettability without modifying surface roughness. The modification of the chemical properties of the Ti surfaces while preserving surface roughness could represent an attractive option for the enhancement of surface properties and the cell response.
12:00 PM - HH9.10
Polydiacetylene-zinc Oxide Nanocomposite Thermochromic Sensors.
Anitha Patlolla 1 , James Zunino 2 , Zafar Iqbal 1
1 Chemistry and Environmental Science, New Jersey Institute of Technology, Newark, New Jersey, United States, 2 U.S. Army Armament Research, Development and Engineering Center, RDAR-MEE-M,, Picatinny Arsenal, New Jersey, United States
Show Abstract Thermochromic reversibility and irreversibility behavior of polymeric 10,12-pentacosadiynoic acid (poly-PCDA) polydiacetylene (PDA) nanocomposites with nanocrystalline inorganic oxides, such as zinc oxide (ZnO), titanium oxide (TiO2), zirconium oxide (ZrO2) and mixed zinc and zirconium oxide, has been studied using resonance Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), extended X-Ray absorption fine structure (EXAFS), X-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC). It was observed that poly-PCDA nanocomposites prepared with nanocrystalline ZnO displayed complete reversibility of the blue to red chromatic transition. In contrast, the chromatic blue to red transition in PDA nanocomposites of TiO2 and ZrO2 remain irreversible. Changes in the terminal carboxylic groups on poly-PCDA in relation to the thermochromic reversibility of the blue to red chromatic transition have been investigated. The results show that salt formation with enhanced hydrogen bonding at head group is essential for thermochromic reversibility or complete recovery of the length of the conjugated π electron chain following thermal stimulus. The crystallite size of ZnO is shown to determine the thermochromic behavior of the poly-PCDA-ZnO nanocomposites. Mixing ZnO with ZrO2 in the nanocomposite controllably slows down the reversing red to blue transition as indicated by Raman, FTIR and XRPD data. The results of this comprehensive investigation allows for the first time the design of reversible sensors based on PDA-ZnO nanocomposites.