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