Richard A. Vaia Air Force Research Laboratory
Jan Genzer North Carolina State University
Gareth H. McKinley Massachusetts Institute of Technology
Nelson Tabiryan Beam Engineering for Advanced Measurements Company
A1: Dynamic Modulus, Shape Memory and Gels I
Monday AM, November 27, 2006
Room 203 (Hynes)
9:00 AM - **A1.1
Morphing Aircraft Systems (MAS).
Brian Sanders 1 Show Abstract
1 , AFRL/VASA, Wright-Patterson AFB, Ohio, United States
9:30 AM - **A1.2
Responsive Liquid Crystalline Networks.
Patrick Mather 1 , Kelly Burke 1 , Ingrid Rousseau 2 , Haihu Qin 1 2 , Alison Oreh 3 , Blayne McKenzie 1 , Stuart Rowan 1 Show Abstract
1 Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, Ohio, United States, 2 Polymer Graduate Program, University of Connecticut, Storrs, Connecticut, United States, 3 , Hathaway Brown School, Shaker Heights, Ohio, United States
10:00 AM - A1.3
Tunability of Acoustic Band Gaps in Strongly Nonlinear Phononic Crystals.
Vitali Nesterenko 1 2 , Chiara Daraio 3 , Jeonghoon Kim 2 , Siyin Wang 1 , Eric Herbold 1 Show Abstract
1 Mechanical and Aerospace Engineering, University of California San Diego, La Jolla, California, United States, 2 Materials Science and Engineering Program, University of California San Diego, La Jolla, California, United States, 3 Aeronautics and Applied Physics, Caltech, Pasadena, California, United States
10:30 AM - A1.5
Novel Activation and Deformation Mechanics of Reinforced Shape Memory Polymer Composites for Morphing Aerostructures.
David Phillips 1 , Fazeel Khan 2 , Matthew Negilski 1 , Gabriel Jacobson 1 , Jeff Baur 1 Show Abstract
1 Materials and Manufacturing Directorate, Air Force Research Laboratories, Wpafb, Ohio, United States, 2 Mechanical Engineering, Miami University, Oxford, Ohio, United States
Current adaptive structures, such as morphing air vehicles, rely on an anisotropic combination of rigidity and extensibility to enable large dimensional changes via an actuated substructure constructed from existing materials. Future responsive structures will likely integrate several active material technologies into hierarchical structured composites that operate synergistically. Since current variable stiffness materials, such as Shape-Memory Polymers (SMP), vary in modulus between that of a thermoplastic and a rubber by heating past the glass transition temperature, reinforcement must be incorporated to obtain the high specific modulus values typical of most aerospace structural materials. However, the traditional method of reinforcement with high modulus fibers limits the ability of the polymer composite to deform while in the rubbery state. Similarly, direct heating of an entire structure may be impractical. Therefore, it is more desirable to employ adaptive polymer composites that either use variable stiffness reinforcement or mechanized structures in conjunction with novel activation to achieve the desired properties. Within this presentation we will discuss recent results from our efforts to incorporate novel reinforcement and activation of SMP’s, including reversibly networked particles, reinforced negative Poisson’s ratio (auxetic) cell structures, spatially-resolved induction heating, and/or embedded microfluidic networks.
11:15 AM - **A1.6
Polymer Nanocomposites in Motion: Remote Actuators.
Eugene Terentjev 1 Show Abstract
1 Physics, Cambridge University, Cambridge United Kingdom
This talk will concentrate on dispersion and alignment of carbon nanotubes in polymer matrix, and the remarkable new properties of the resulting active material. Some of the nanotube responses to such stimuli as light and heat, in particular the effect of buckling, remain poorly understood. However, their action in polymer nanocomposites is amplified and transferred to the macroscopic level, resulting in light- and heat-induced mechanical actuation. Such actuation is equilibrium (reversible on cycling the stimulus) and therefore opens new avenues for micro-mechanical engineering design. On the fundamental level, we begin to understand how and why the nanotubes respond to light and heat by conducting studies on individual tubes, and their mats and fibers.
11:45 AM - A1.7
Knots with Stiff Filaments.
Olivier Pierre-Louis 1 , Riccardo Gallotti 1 Show Abstract
1 Laboratoire de Spectrometrie Physique, CNRS, Saint Martin d'Heres France
12:00 PM - A1.8
Novel Actuation of TEMBO®, Thermoset-Epoxy Shape Memory Polymers.
Steven Arzberger 1 , Naseem Munshi 1 , Craig Hazelton 1 , Mark Lake 1 Show Abstract
1 , Composite Technology Development, Inc. (CTD), Lafayette, Colorado, United States
TEMBO® shape memory polymers (SMPs) are smart materials that can ”freeze” and release strain in response to a specific thermo-mechanical load cycle. Incorporation of these materials into continuous-fiber-reinforced Elastic Memory Composite (EMC) format enables the development of lightweight actuators and deployable structures with greater deployed structural stiffness, packaging efficiency, and deployment force than achievable using other smart-material technologies. Current EMC are largely actuated through embedded resistive wire heating. In many cases, especially for larger structures, embedded wire heaters are undesirable as they increase complexity, mass, and cost. As a result, several wireless actuation technologies have been developed for TEMBO® SMPs and EMC components including: (1.) passive in space solar heating, (2.) electromagnetic-field-induced heating, and (3.) infrared-light-induced heating. The proposed paper will discuss these wireless heating concepts and significant opportunities for their application.
12:15 PM - A1.9
Carbon Nanotubes Foams as Novel Highly Nonlinear Springs and Dynamic Energy Dissipation Layers.
Chiara Daraio 2 , Vitali Nesterenko 1 , Sungho Jin 1 Show Abstract
2 Aeronautics and Applied Physics, Caltech, Pasadena, California, United States, 1 Mechanical and Aerospace Engineering, University of California San Diego, La Jolla, California, United States
12:30 PM - A1.10
Constitutive Modeling of Shape Memory Polymers and its Application to Shape Changing Biomedical Device Design.
H. Jerry Qi 1 , Francisco Castro 1 , Chris Yakacki 1 , Robin Shandas 1 , Ken Gall 2 Show Abstract
1 Mechanical Engineering, University of Colorado, Boulder, Colorado, United States, 2 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
A2: Control Release
Monday PM, November 27, 2006
Room 203 (Hynes)
2:30 PM - A2.1
Stimuli-responsive Polymer Thin Films from Polyelectrolyte Multilayers: From Hysteretic Gating of Membranes to Magnetic Nanotubes.
Daeyeon Lee 1 , Adam Nolte 2 , Michael Rubner 2 , Robert Cohen 1 Show Abstract
1 Chemical Engineering Department, MIT, Cambridge, Massachusetts, United States, 2 Department of Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States
We demonstrate that layer-by-layer assembled polyelectrolyte multilayers on track-etched polycarbonate (TEPC) membranes can be utilized to create stimuli responsive membranes and magnetic nanotubes. First, multilayers comprising poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS) assembled at a high pH condition were coated onto TEPC membranes to create pH-responsive membranes that show hysteretic gating behavior. The trans-membrane flux exhibits a large discontinuous and reversible transition as a function of solution pH. The hysteretic gating property of the multilayer-modified TEPC membrane was utilized to achieve either a “closed” or “open” state at one pH condition depending on the pretreatment history, thereby enabling either the retention or passage of high-molecular weight polymers by varying the membrane pretreatment condition. The degree of swelling of the pore-confined multilayers as estimated by simple models was significantly smaller than the swelling of the multilayers on planar substrates under the same conditions. Second, heterostructured superparamagnetic magnetic tubes with sub-micron dimensions could be created by depositing additional layers of iron oxide nanoparticles with PAH into the inner surfaces of PAH/PSS multilayer-modified pores of TEPC membranes. The magnetic nanotubes could be isolated from the template (i.e., TEPC membranes) by dissolving the membranes in an organic solvent. The magnetic nanotubes could be successfully used to separate (or remove) a high concentration of dye molecules from solution by activating the nanotubes in acidic solution. The release of the anionic molecules in physiologically relevant buffer solution showed that while bulky molecules release slowly, small molecules release rapidly from the multilayers.
2:45 PM - A2.2
Controlled Electro-Dissolution of Polyelectrolyte Multilayers: a Platform Technology towards the Surface Initiated Delivery of Drugs
Fouzia Boulmedais 1 2 3 , Clarence Tang 2 3 , Beat Keller 2 , Janos Voros 3 Show Abstract
1 , Institut Charles Sadron, CNRS UPR 22, Strasbourg France, 2 , Swiss Federal Laboratories for Materials Testing and Research (EMPA), Dübendorf Switzerland, 3 Laboratory for surface science and technology, Swiss Federal Institute of Technology (ETH) , Zurich Switzerland
3:00 PM - A2.3
Controlled Electrochemical Release of Layer by Layer Assemblies.
Nicole Zacharia 1 , Paula Hammond 1 Show Abstract
1 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
3:15 PM - A2.4
In Vitro Degradation of Poly(Lactic-co-Glycolic) Acid Block Copolymers.
Alberto Saiani 1 2 , Elisabeth Vey 1 , Aline Miller 2 , Mike Claybourn 3 Show Abstract
1 School of Materials, The University of Manchester, Manchester United Kingdom, 2 School of Chemical Engineering and Analytical Science, The University of Manchester, Manchester United Kingdom, 3 , AstraZeneca, Macclesfield United Kingdom
4:30 PM - A2.5
Exploiting Polymeric Self-Assembly as a Route to Improved Gene and Drug Delivery Systems.
Kris Wood 1 , Robert Langer 1 , Paula Hammond 1 Show Abstract
1 Chemical Engineering, MIT, Cambridge, Massachusetts, United States
4:45 PM - A2.6
A New Class of Enzyme Responsive Polymer Hydrogels for Drug Delivery.
Paul Thornton 1 , Rein Ulijn 1 Show Abstract
1 Interdisciplinary Biocentre, The University of Manchester, Manchester United Kingdom
5:00 PM - A2.7
Hydrogel Beads that Respond to Cell Secreted Enzymes.
Robert Mart 1 , Rein Ulijn 1 Show Abstract
1 Manchester Interdisciplinary Biocentre, The University of Manchester, Manchester United Kingdom
Cells may secrete different proteases into the extracellular matrix depending on their state. As such, these proteases may be used as markers of different points in cell cycles or disease states. We have investigated the use of hydrogel beads as sensors to detect these proteases. Polyethyleneglycol acrylamide (PEGA) copolymer beads are non-fouling and contain free amine groups which may be modified with peptide sequences. By appending peptide sequences that are good substrates for proteolytic enzymes, beads can be constructed that respond selectively to the presence of that enzyme. By careful design of the peptide sequences, beads may be engineered to swell, increasing their accessibility to the enzyme, or collapse, entrapping the enzyme within. These methodologies have potential applications in drug delivery, wound healing and purification applications in addition to biomolecular sensing.
5:15 PM - A2.8
Synthesis and Responsive Properties of Dibenzoylmethane Metallobiomaterials.
Cassandra Fraser 1 , Jianbin Chen 1 , Anne Pfister 1 , Yin Jie Chen 1 Show Abstract
1 Chemistry, University of Virginia, Charlottesville, Virginia, United States
5:30 PM - A2.9
Enzyme Catalysis: Tool to Make and Break Amygdalin Hydrogelators from Renewable Resources - A Delivery Model for Hydrophobic Drugs
Praveen Kumar Vemula 1 , George John 1 Show Abstract
1 Department of Chemistry, City College of the City University of New York, New York, New York, United States
5:45 PM - A2.10
Hyaluronan-Based Hybrid Hydrogels with Tunable Mechanical Properties for Soft Tissue Regeneration
Xinqiao Jia 1 , Yoon Yoe 2 , Nurettin Sahiner 1 , Amit Jha 1 Show Abstract
1 Materials Science and Engineering, University of Delaware, Newark, Delaware, United States, 2 Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Mechanical forces play a decisive role during development of tissues and organs, during remodeling following injury as well as in normal function. As a result, cells can feel and respond not only to mechanical stresses, but also to the stiffness of their substrates. Biocompatible hydrogels with tunable mechanical properties and rapid mechano-responsiveness are promising candidates for biomedical applications. We have developed hyaluronan (HA)-based soft hydrogel particles (microgels and nanogels) with controlled size, chemistry and structure. HA microgels were prepared by in situ cross-linking of chemically modified HAs within an inverse microemulsion stabilized by Span 80, followed by solvent evaporation; whereas HA nanogels were synthesized by in-situ crosslinking of HA with divinyl sulfone within reverse micelles stabilized by sodium bis(2-ethylhexyl)sulfosuccinate. In vitro cytotoxicity studies using vocal fold fibroblasts indicate that these hydrogel particles are essentially non-toxic. HA microgels exhibit residual functional groups that can be used as reactive handles for subsequent crosslinking with other functional polymers, giving rise to macroscopic hydrogels (macrogels) with tunable viscoelasticity. On the other hand, free radical polymerization/crosslinking of acrylamide in the presence of HA nanogels resulted in interpenetrating networks that are enzymatically stable and mechanically elastic. Controlled release of pharmaceutically active compounds was achieved through their anchorage at predetermined locales of the particulate hydrogel system. Mechano-responsive hydrogels were generated by crosslinking HA microgels/nanogels using complementary peptide nucleic acid with defined sequence length. Mechanical measurements indicate that these double crosslinked hydrogel networks exhibit tunable viscoelastic responses. These materials hold great promise for soft tissue regeneration.
A3: Poster Session
Monday PM, November 27, 2006
Exhibition Hall D (Hynes)
9:00 PM - A3.1
Water Interaction with the Ferroelectric Copolymer PVDF-TrFE and the Dipole Oriented Polymer PMVC.
Carolina Ilie 1 , Peter Jacobson 1 , Luis Rosa 1 , Ivan Yakovkin 2 , Matt Poulsen 1 , Damireddi Sahadeva Reddy 3 , James Takacs 3 , Stephen Ducharme 1 , Peter Dowben 1 Show Abstract
1 Physics and Astronomy, University of Nebraska - Lincoln, Lincoln, Nebraska, United States, 2 Physics, Institute of Physics of National Academy of Sciences of Ukraine, Kiev Ukraine, 3 Chemistry, University of Nebraska - Lincoln, Lincoln, Nebraska, United States
We compare water adsorption and absorption on the crystalline ferroelectric copolymer poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE 70:30) and the dipole ordered polymer poly(methylvinylidene cyanide) PMVC. Both films, prepared by the Langmuir Blodgett technique from a water subphase, were crystalline, as determined by STM and band structure . Several different adsorption sites have been identified by thermal desorption spectroscopy for each of the polymers. For PVDF-TrFE, one adsorbed water species resembled ice, and a surface bulk absorbed species were identified. Two bulk absorbed water species were observed for PMVC. The absorbed water species interact more strongly with PVDF-TrFE than with PMVC. The absorption of water is believed to distort the polymer chain placement for both polymers. The concordance between the experimental data and the theoretical calculations of the potential energy of the water molecule between two polymer chains is discussed in each case.The occurrence of the steric effects during the water desorption process was investigated by undertaking angle-resolved thermal desorption. The PVDF-TrFE copolymer shows large deviations from the expected  cosβθ distribution with the thermal desorption of water when illuminated with light. Water desorption from PMVC deviates from the cosβθ distribution without illumination.References1. Xiao, Jie, Rosa, Luis G., Poulsen, M., Feng, D.-Q., Sahadeva Reddy, D., Takacs, J. M., Cai, Lei, Zhang, Jiandi, Ducharme, S., and Dowben, P. A., J. Phys. Cond. Matter , 18, L155-L161, 2006. 2. Steinrück, H. P., Winkler, A., Rendulic, K. D., J. Phys. C: Solid State Phys., 17, L311-L316, 1984.
9:00 PM - A3.10
Electrostatic Effects on the Shape of Self-assembled Charged Lipid Membranes.
Graziano Vernizzi 1 , Monica Olvera de la Cruz 1 Show Abstract
1 Materials science and engineering, Northwestern University, Evanston , Illinois, United States
9:00 PM - A3.11
Density Fluctuation in Coulombic Colloid Dispersion: Self-Assembly of Lipid A-Phosphates.
Chester Faunce 1 , Henrich Paradies 1 Show Abstract
1 Joule Physics Laboratory, Institute for Materials Research, The University of Salford, Manchster, M5 4WT United Kingdom
There is considerable interest in understanding the properties of lipopolysaccharides and phosphorylated/unphosphorylated lipid A as well as their nontoxic analogues, because of its release in the course of bacterial infections and inhibition of a septic shock. Scattering experiments and theoretical concepts based on liquid state theory were used to explore the structure of complex aqueous colloidal suspensions i.e. lipid A diphosphate and analogues. Electron microscopy, static and dynamic light scattering, osmotic pressure and SAXS measurements were performed on lipid A-diphosphate dispersions from E. coli. Experiments were performed at low ionic strength (0.001M NaCl) and over a volume fraction range of 1.5 x 10-5<Φ< 5.75 x 10-3 (1-3).The particle surface charge was determined by comparing S(Q=0) obtained from SAXS and LS after correction for polydispersity (ρ=0.072), and for the mole fractions of a 3-subcomponent system. Ip(Q) and S(Q) were calculated from liquid state theory. The discrepancy between the number of total sites (2550)e and the structural colloidal charge (756)e indicates few sites are ionized (2).Higher order peaks (LS and SAXS) made it possible to determine the nature of the structures in the presence of Ca2+, Mg2+, K+, Na+ ions (3), as well as lipid A diphosphate analogues (4)in more detail. The parameters obtained from experimental and liquid state theory results and the thermodynamics of the phase transition suggests the existence of a transition from a liquid to a FCC structure. This FCC subphase can be transformed to a BCC lattice by increasing the salt concentration (T=const). The Q dependence of the scattering of the liquid phase and the crystalline BCC phase are very similar with the liquid S(Q) peak close to Q = Q (110). Colloidal crystals of lipid A-diphosphate-Ca2+ and K+ could be assigned to a FCC lattice with a=56.30 and a=55.90 nm for the Ca2+ and K+ salts, respectively. The scattering profiles for the Mg2+ and Na+ salts can be assigned to a BCC lattice with a=45.50 nm for the Mg2+ salt and a=41.50 nm for the sodium salt of lipid A-diphosphate. The BCC structures were not anticipated since for charged colloidal particle systems FCC structures are more often found. The crystal structures of lipid A diphosphate are influenced by a number of different factors, these include polydispersity, nature of cations, the ionic strength of the solution (0.1-1.0 mM NaCl), number density, and temperature. The shape of the nanocrystals are either cubic or rhombohedral, and conforms to a trigonal or hexagonal unit cell with a=3.65 nm and c=1.97 nm. This assembly exhibits a structural periodicity with a spacing of 0.65 nm which are four times the size of the adopted unit cell of lipid A phosphate (2).(1) C. A. Faunce et al., P. J. Phys. Chem., 107, 8414(2003.(2) C. A. Faunce et al., J. Phys. Chem., 107, 9943 (2003).(3) M. Thies et al., J. Chem. Phys., 116, 3471 (2002).(4) C. A. Faunce et al. J. Chem. Phys., 122, 214727 (2005).
9:00 PM - A3.12
Direct Measurement of the Elastic Properties of the Wiseana Iridovirus (WIV) Capsid using Brillioun Spectroscopy.
Stephen Wargacki 1 4 , A. Sokolov 5 , A. Kisliuk 5 , T. Gorishnyy 2 , E. Thomas 2 , V. Ward 3 , R. Vaia 1 Show Abstract
1 , Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States, 4 , National Research Council, Washington, District of Columbia, United States, 5 , University of Akron, Akron, Ohio, United States, 2 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 , University of Otago, Dunedin New Zealand
The proteinacious capsids of virus particles are of great interest for their potential as templates or scaffolds to direct the growth of secondary structures for various sensing, energy harvesting, and photonic devices. However, due to their size (10’s-100’s nms) and complex structure (symmetrically repeating protein subunits); the mechanical properties of viruses and viral films has yet to be directly measured. We measured the phononic spectra of virus capsids assembled on an aluminum substrate using Brillouin Light Scattering at different scattering wave vectors. The phononic spectrum provides a direct measurement of the mechanical properties of individual viruses as well as that of the collective assemblage. By controlling the levels of humidity in the atmosphere around the films, the impact of water on the elastic properties of the virus and assemblage has been examined. Understanding the mechanical properties of the viruses is critical for the reliable utilization of the subsequent templates and assemblies for device fabrication and performance, as well as contributing to the understanding of the impact of capsid flexibility and rigidity on the process of cellular infection by viruses.
9:00 PM - A3.13
Formation and Evolution of Buckling Patterns in Elastic Shells.
Ashkan Vaziri 1 , L. Mahadevan 1 Show Abstract
1 Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
9:00 PM - A3.14
Enhancing Thermoplastic Shape Memory Polyurethanes via Nanoreinforcement.
Shawna Liff 1 2 , Gareth McKinley 1 Show Abstract
1 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Institute for Soldier Nanotechnologies, Cambridge, Massachusetts, United States
9:00 PM - A3.15
Soft Segment Orientation Effects on the Morphology and Mechanical Properties of Polyurethanes.
Ryan Waletzko 1 , Paula Hammond 1 Show Abstract
1 Chemical Engineering, MIT, Cambridge, Massachusetts, United States
A series of polyurethane elastomers were designed with varying poly(ethylene oxide) (PEO) lengths and hard segment contents. Segmented polyurethanes containing higher soft segment molecular weight (4600 g/mol) demonstrated a lamellar morphology, a result of the highly crystalline hard and soft domains. Polyurethanes containing lower molecular weight PEO (1000 g/mol) showed less microphase segregation at similar hard segment contents. As the hard segment content was increased, hard domain crystallinity was enhanced, demonstrated by a shift in the morphology from a soft segment continuous to an interconnected microstructure. High molecular weight PEO-containing polyurethanes showed a tendency to neck upon deformation, which likely resulted from the largely crystalline soft domains. Low molecular weight PEO-containing polyurethanes (1000 g/mol) did not show a tendency to neck during deformation due to the lesser extent of microphase segregation.
9:00 PM - A3.16
Plastic Effect for Wrinkling Pattern of Thin Au Film on Polymer Substrate.
Jeong Yun Sun 1 , Myoung-Woon Moon 2 , Kyu Hwan Oh 1 Show Abstract
1 Material Science & Engineering, Seoul National Univ., Seoul Korea (the Republic of), 2 Division of Engineering and Applied Sciences, Harvard University, Boston, Massachusetts, United States
We analyzed wrinkling morphologies of thin metal film on polymer substrate affected by plastic deformation under high compressive strain, accompanying a hierarchical wrinkling structure. We deposited thin Au film in the range of 1nm to 200nm on pre-strained polymer substrate with home-made device, forming wrinkles as releasing polymer substrate. The wavelength has been ranged from 0.5micron to 5micron at the strain lower than 30%, which is associated with fundamental wrinkling solution. Above 30%, wrinkling shows plastic deformation that valley of wrinkling would be hinged and adjacent wrinkle becomes merged together. After 50% compressive strain, we restored the strain back to 0% by pulling. TEM analysis for 10 and 50 nm thick film confirmed that the distorted (redistribution) crystalline structure at near valley and peak of wrinkles lead permanent structural change in the film.
9:00 PM - A3.17
Cross-Linked Liquid Crystal Mesostructures for Electro-Rheological Fluids.
Darran Cairns 1 , Matthew Shafran 1 Show Abstract
1 Mechanical & Aerospace, West Virginia University, Morgantown, West Virginia, United States
9:00 PM - A3.18
Electrical Assembly of Microbridge Based Detectors For Protein Sensing.
Vindhya Kunduru 1 , Sudhaprasanna Padigi 1 , Shalini Prasad 1 Show Abstract
1 , Portland State University, Portland, Oregon, United States
9:00 PM - A3.19
Optimizing Responsive Characteristics of Polymer Nanocomposites Using Electromagnetic Fields to Prescribed, Non-isotropic Distributions of Nanoparticles.
Hilmar Koerner 1 , Richard Vaia 2 , Wei Lu 3 , Evangelos Manias 4 , Georgios Polizos 4 , Ramanan Krishnamoorti 5 , Zoubeida Ounaies 6 Show Abstract
1 , Universal Technology Corp., Wright-Patterson AFB, Ohio, United States, 2 , Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States, 3 , University of Michigan, Ann Arbor, Michigan, United States, 4 , Penn State University, University Park, Pennsylvania, United States, 5 , University of Houston, Houston, Texas, United States, 6 , Texas A&M University, College Station, Texas, United States
To optimize actuator characteristics of nanocomposites containing high aspect ratio nanoparticles (layered silicates, nanotubes, ZnO rods), a prescribed, non-isotropic distribution (orientational and spatial) of the nanoparticles within the matrix is necessary to maximize coupling between the particle's alignment and the matrix's dielectric response. This is especially true when a unidirectional control stimulus is not co-linear with the desired response direction. At present, only limited methodologies exist that provide the ability to spatially 'engineer, design and tailor' nanocomposite morphology to the degree that is expected for traditional fiber reinforced composites. Herein, AC electrokinetics will be discussed as an approach to provide non-invasive, spatial and orientational control of high aspect ratio oxide nanoparticles in polymers (elastomers and glassy thermosets). Specifically, we will compare theoretical predictions based on a continuous phase field model to experimental observations of dielectrophoretic alignment of large aspect ratio oxide nanoparticles with complex dielectric characteristics. The simulation reveals remarkably rich dynamics and suggests a significant degree of experimental control in growing ordered nanoscale structures. Initial experiments on layered silicates suggest that the primary cause is due to induced dipoles (image charges) on the dielectric inorganic platelets. The degree of orientation depends on the electric field frequency and strength. Additionally, the impact of nanoparticle concentration and alignment on global response of these nanocomposites will be summarized. The resulting experimental validation of the theoretical predictions provides a powerful approach to tune nanocomposite morphology for optimizing the responsive characteristics based on predictions of the optimal nanoparticle orientation.
9:00 PM - A3.2
Structure/Property Relationships in Polypyrrole Actuators.
Rachel Pytel 1 , Vahik Krikorian 1 , Edwin Thomas 1 , Ian Hunter 2 Show Abstract
1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Polypyrrole has been extensively studied as an electroactive material, but these studies have provided little insight to the influence that morphology has on actuation at the nanoscale. We utilize different modes of deformation to impart orientation textures on free-standing polypyrrole films that can be observed via x-ray diffraction and electronic resistance measurements. Certain textures enhance pathways for ion transport between polymer chains, resulting in an anisotropic electroactive strain response that can be immediately harnessed when making polypyrrole-driven devices. This response provides valuable insight to the mechanism of polypyrrole actuation on the nanoscale, supporting a mechanism where counterions migrate to locations between the oriented polymer chains. However, electron and x-ray diffraction have shown there is little change in the polymer structure upon the insertion and expulsion of counterions at relevant timescales. In order to elucidate the elements of polypyrrole microstructure responsible for actuation, free-standing films are deposited using a variety of solvents and counterions. Films deposited from different recipes show comparable electroactive responses, even though X-ray diffraction and scanning electron microscopy show considerable differences in the microstructure and morphology of the films. By comparing the actuation of films with widely varying morphologies, the elements of polypyrrole structure most beneficial to actuation can be exposed. Detailed understanding of these morphological features will help us process polypyrrole more intelligently, enhancing these features to achieve a larger and faster electroactive response.
9:00 PM - A3.20
Optical Self-trapping and Spontaneous Pattern Formation of White Light in a Free-radical Polymerization System.
Kailash Kasala 1 , Kalaichelvi Saravanamuttu 1 Show Abstract
1 Chemistry, McMaster University, Hamilton, Ontario, Canada
9:00 PM - A3.21
Modeling Nanoparticle Dynamics: Towards Controlled Assembly Using Dielectrophoresis.
Michael Vahey 1 , Robert Barsotti 2 , Ryan Wartena 2 , Joel Voldman 1 , Yet-Ming Chiang 2 , Francesco Stellacci 2 Show Abstract
1 Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
9:00 PM - A3.23
Photo-Responsive Colloids: Modifying Surface Charge and Assembly via Light.
Jacinta Conrad 1 , Nathan Bowling 2 , Joshua Ritchey 2 , Ali Mohraz 1 , Kyle Plunkett 2 , Jeffrey Moore 2 , Jennifer Lewis 1 Show Abstract
1 Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
9:00 PM - A3.24
A General Approach to Patterning Micro- and Nanostructures.
Nathanael Sieb 1 , Byron Gates 1 Show Abstract
1 Chemistry, Simon Fraser University, Burnaby , British Columbia, Canada
9:00 PM - A3.25
Making Azobenzenes Fluorescent: Substituent Effects on Light-Driven Self-Assembly of Azobenzenes.
Mina Han 1 , Yuuki Hirayama 1 , Masahiko Hara 1 Show Abstract
1 Local Spatio-Temporal Functions Laboratory, Frontier Research System, RIKEN, Wako Japan
9:00 PM - A3.26
Novel Silicon-Elastomers for Advanced Soft Lithography.
Kyung Choi 1 Show Abstract
1 , Bell Labs, Lucent Technologies, Murray Hill, New Jersey, United States
9:00 PM - A3.27
Preparation of New Macroporous Poly(divinylbenzene) Gels via Living Radical Polymerization.
Kazuyoshi Kanamori 1 , Kazuki Nakanishi 1 , Teiichi Hanada 1 Show Abstract
1 Dept. of Chemistry, Graduate School of Science, Kyoto University, Kyoto Japan
Monolithic macroporous materials are widely attractive class of materials that supply macroporosity suitable for rapid liquid and gas transportations with large accessible surface area. Macroporous organic gels are conventionally prepared from radical polymerization of vinyl monomer(s) together with cross-linker(s), and have been developed especially in the field of separation, ion exchange, catalysts. However, a fine control of pore size, volume and porosity is still rather difficult despite pile of efforts so far. In the present report, we adopted living radical polymerization to tailor well-defined macroporous polymer gels because we attribute the fail of the fine control of the pores to the robust reaction mechanism of the conventional free radical polymerization. In the solution polymerization using the conventional free radical initiator, small (usually sub-micron to micron-sized) particles segregate from the solvent by an abrupt increase of local degree of polymerization (DP), leading to a contingent formation of macropores as interstices between segregated particles. In living radical polymerization, on the other hand, since such an abrupt increase of local DP is avoided by the stepwise increase of DP against time, particles segregation will be unlikely to occur.In our experiments, in order to obtain macroporous morphologies, we introduced a polymeric agent poly(dimethylsiloxane) (DMS) that induces spinodal decomposition during TEMPO-mediated living radical polymerization reaction of divinylbenzene (DVB). Other chemicals, 1,3,5-trimethylbenzene (TMB) and acetic anhydride (Ac2O) were used as a (good) solvent and a polymerization accelerator, respectively. As a radical initiator, 2,2’-azobis(isobutyronitrile) (AIBN) or benzoyl peroxide (BPO) were employed. By adjusting compositions appropriately, we obtained well-defined macroporous gels with bicontinuous structure presumably developed by spinodal decomposition. Macropore size can be controlled from sub-microns to a few tens microns with typical porosities up to 70%, and pore size distribution is found to be quite sharp. Moreover, macropore size and volume are found to be independently tunable simply by changing starting compositions: The concentration of DMS determines pore sizes, and that of TMB decides pore volumes. Thus it can be deduced that phase separation occurs between the polymerizing DVB and DMS in a viscous liquid where TMB acts as a co-solvent. Thermal and mechanical stabilities have been evaluated on dried poly(divinylbenzene) gels and it was found good thermal durability up to 300°C and excellent mechanical strength which is comparable to sintered macroporous silica gels with the similar morphology and porosities. Heat-treatment at 200°C makes the DVB-derived polymer gels even harder, which is due to the additional thermal coupling reaction of pendant vinyl groups that were not reacted during the solution polymerization.
9:00 PM - A3.28
Early-Time, In-Situ Characterization of Triggered β-hairpin Self-Assembly into Hydrogel Networks.
Tuna Yucel 1 3 , Joel Schneider 2 , Darrin Pochan 1 3 Show Abstract
1 Materials Science and Engineering, University of Delaware, Newark, Delaware, United States, 3 Delaware Biotechnology Institute, University of Delaware, Newark, Delaware, United States, 2 Chemistry and Biochemistry, University of Delaware, Newark, Delaware, United States
Water soluble, 20-residue peptides were designed to undergo intramolecular folding into β-hairpins and consequently self-assemble intermolecularly into hydrogel networks. Peptide folding and self-assembly could be triggered via biologically relevant stimuli such as pH, temperature and salt concentration. Substantial responsiveness of assembly kinetics towards external stimuli and peptide concentration was demonstrated and utilized in order to enable real and reciprocal space characterization of the system with a set of complimentary techniques: Dynamic light scattering monitored the intermolecular self-assembly process, cryoTEM and SANS monitored the self-assembled nanostructure formation, while circular dichroism spectroscopy monitored the intramolecular folding of peptides. Peptides immediately began to fold and self-assemble (i.e. downhill polymerize) into fibrillar nanostructures that locally branched and entangled to form clusters. These clusters eventually interpenetrated to form a percolated network gel. Even though individual techniques taken on their own indicated a nucleation and growth mechanism (i.e. a lag phase apparent in light scattering), only by combining the diverse molecular and nanostructure characterization techniques at the same time points can one accurately characterize the early time, triggered self-assembly. The data collected by different characterization techniques on early stages of peptide assembly will be discussed in conjunction with the proposed self-assembly mechanism.
9:00 PM - A3.29
Neutron Scattering Study of Shear Induced Structure in Poly(ethylene oxide)/ Laponite Gels.
Jun Li 1 , Steven Schwarz 1 , Jun Jiang 2 , Chunhua Li 2 , Min Lin 2 , Miriam Rafailovich 2 , Jonathan Sokolov 2 Show Abstract
1 physics, Queens College, City University of New York , Flushing, New York, United States, 2 Materials Science and Engineering, SUNY Stony Brook, Stony Brook, New York, United States
9:00 PM - A3.3
Processing and Properties of SWNT/PMMA Composites.
Jing Liu 1 , Satish Kumar 1 Show Abstract
1 , Georgia Institute of Technology, Atlanta, Georgia, United States
9:00 PM - A3.30
Controlled Release of Molecules from the poly(dimethyl siloxane)-mesoporous Silica Composite Triggered by Ultrasound.
Emiko Otsuka 1 , Etsuko Taomo 2 , Hyun-Jong Kim 3 , Itaru Honma 3 , Yumiko Hirashima 2 , Atsushi Suzuki 1 Show Abstract
1 Yokohama National University, Graduate School of Environment and Information Sciences, Yokohama Japan, 2 Yokohama National University, Faculty of Education and Human Sciences, Yokohama Japan, 3 , National Institute of Advansed Industrial Science and Technology , Tsukuba Japan
The mesoporous silica was prepared by replicating the network structure of hydrogels in sol-gel derived silica matrix. The pore sizes of silica were adjusted 3.5,7.0,15.8nm by increasing amount of template polymer. The ibuprofen as a model molecule was impregnated into the mesoporous silica by dissolving in hexane and the amount of ibuprofen was measured by a thermogravimetry. The ibuprofen-loaded silica powder was incorporated in poly(dimethyl siloxane) (PDMS) solution and the curing agent was added to the mixture for the cross-linking of PDMS, which was dried at 65 degrees for 48hours. The composite was put in a vial with water, and the change in the concentration of ibuprofen in the water was analyzed using a UV-visible spectrometer. The water was repeatedly exchanged in a constant interval at room temperature. After the release rate saturated, the vial was immersed in the sonic bath with the freqiencies of 39kHz. The ultrasound was repeatedly irradiated in a constant interval, and the water was repeatedly exchanged after each irradiation. The concentration of ibuprofen in the water was measured before and after the respective irradiation. As a result, the release rate depended not only on the pore size of mesoporous silica but also on the network structure of PDMS matrix determined at the cross-linking. The technique to realize a controlled release of molecules using the present system will be proposed on the basis of the physical and chemical properties of the mesoporous silica and the PDMS matrix.
9:00 PM - A3.31
Control of Adhesion Properties of Swollen Hydrogels by Changing Environment Conditions.
Daisuke Sakasegawa 1 , Atsushi Suzuki 1 Show Abstract
1 Yokohama National University, Graduate School of Environment and Information Sciences, Yokohama Japan
9:00 PM - A3.32
Temperature and pH Responsive Polyamides with Tailored LCSTs.
Theresa Foley 1 , Evangelos Manias 1 Show Abstract
1 Materials Science & Engineering, Penn State University, University Park, Pennsylvania, United States
9:00 PM - A3.33
Modeling Release of Nanoparticles from Mobile Microcapsules.
Anna Balazs 1 , Rolf Verberg 1 , Alexander Alexeev 1 Show Abstract
1 Chemical Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
9:00 PM - A3.34
Molecular Dynamics Simulations of Micellar Dynamics and Stability.
Pawel Weronski 1 2 , Yi Jiang 1 , Steen Rasmussen 3 Show Abstract
1 Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Krakow Poland, 3 Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Polymeric micelles show great promise as tiny drug carriers. They are spheres with diameters of about 50nm, which can facilitate the transport of drugs to some of the smallest capillaries in the body. These nanospheres can be designed to travel to specific sites within the body, release their payload of drug molecules and then degrade. We employ molecular dynamics computer simulations to investigate the dynamics and stability of a micelle composed of surfactant molecules (decanoic acid molecules) under different conditions. Initially, we simulate the self-assembling process of the micelle at pH=9 when all the surfactant molecules are dissociated. We obtain a stable micellar aggregate after 70ns. Its average aggregation number is equal to twenty six. We notice that at high ionic strength of the electrolyte the aggregation number is larger, which results from electrostatic screening of the micelle surface charge and diminished electrostatic repulsion between the micelle and the individual surfactant molecules in the bulk. At neutral pH, when 50% of the surfactant molecules in the micelle are dissociated and 50% are protonated, we observe a systematic grow of the micelle and change of its shape from spherical to oblate spheroidal. We also demonstrate that the repulsive electrostatic interaction between the charged surfactant molecules forming a micelle can lead to micelle division.This work was carried out under the auspices of the National Nuclear Security Administration of the U.S. Department of Energy at Los Alamos National Laboratory under Contract No. DE-AC52-06NA25396.
9:00 PM - A3.36
Study Counterion Effects in the Charged G4 PAMAM Dendrimer Aqueous Solutions by Small Angle Neutron Scattering.
Wei-Ren Chen 1 4 , Lionel Porcar 2 3 , Yun Liu 2 3 , Lee Magid 4 Show Abstract
1 SNS, ORNL, Oak Ridge, Tennessee, United States, 4 Department of Chemistry, University of Tennessee, Knoxville, Tennessee, United States, 2 , NIST Center for Neutron Research, Gaithersburg, Maryland, United States, 3 Department of Material Science and Engineering, University of Maryland, College Park, Maryland, United States
9:00 PM - A3.37
Visualizing Molecular Information by Creating Optical Wavelength-Sized Periodically Ordered Structure in Hydroge.
Yukikazu Takeoka 1 , Takahiro Seki 1 Show Abstract
1 , Nagoya University, Nagoya Japan
9:00 PM - A3.38
Conductive Elastomeric Nanocomposites as Force Sensitive Resistors for an Artificial Hair Cell Device
Michael Arlen 1 , Shane Juhle 1 , Richard Vaia 1 , Jon Engel 2 , Chang Liu 2 Show Abstract
1 MLBP, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio, United States, 2 Electrical and Computer Engineering, University of Illinois, Urbana-Champaign, Urbana, Illinois, United States
Biological sensory receptors are versatile and exceedingly well-adapted mechanical transducer capable of detecting noise, temperature, and pressure. Recent developments in micromachining and patterning have provided the fabrication capabilities necessary to construct biomimetic devices. One example is the two axis artificial hair cell fabricated with conductive nano-filler impregnated polymer force sensitive resistors (FSRs) at the base of a vertical cantilever hair. The role of the FSRs is to transduce the motion of the cilium deflection into resistance changes. Filler dispersion in the polymer matrices and the percolation behavior of the nanocomposites consisting of different nanoparticles varying in size and aspect ratio is examined. Cilium deflection testing of the hair cell sensor showed that the sensitivity of the carbon nanofiber device was 1609 ppm/µm, an improvement by a factor of 7.8 over the carbon black device (245 ppm/µm). The reduced filler load of the MWNT devices also improved the polymer-substrate adhesion. In situ resistance monitoring during uniaxial compression testing was performed on the FSRs and results are discussed. These results demonstrate that the FSRs piezoresistive behavior and durability may be significantly enhanced by high aspect ratio conductive fillers.
9:00 PM - A3.39
Gold Nanoparticle Liquids with an Ionic Organic Corona: Synthesis and Application as Conductive Lubricants for MEMS Technology
Steve Diamanti 1 2 , Steve Patton 1 4 , Emily Seikel 3 , Mark Pender 1 , Andrey Voevodin 1 , Richard Vaia 1 Show Abstract
1 , Air Force Research Laboratories, Wright-Patterson AFB, Ohio, United States, 2 , National Research Council, Washington, District of Columbia, United States, 4 , University of Dayton Research Institute, Datyon, Ohio, United States, 3 , University of Dayton, Dayton, Ohio, United States
Through molecular engineering of the organic-corona (passivation) surrounding inorganic nanoparticles, monolithic hybrid nanoparticles, including silica and iron-oxide, have been fabricated that exhibit glassy or liquid behavior. By minimizing the volume fraction of organic corona necessary to provide the liquid-like behavior at room temperature (and thus maximizing inorganic volume fraction and nanoparticle number density), numerous applications arise including conductive lubricants, solvent-less inks for microfabrication, and compliant electrodes. Focusing on gold nanoparticles, mercaptoethane sulfonate (MES) stabilized gold nanoparticles were coupled to large organic anions, such as Adogen 464 (methyltrialkyl(C8-C10)ammonium chloride) and a PEG-alkyl ammonium salt (cocoalkylmethyl PEG-15 ammonium chloride), through electrostatic attraction. The ionic-liquid analog corona provided functionalized Au nanoparticles that exhibited amphiphilic character (soluble in a wide range of organic solvents) and films with self-healing properties. The nanoscopic size and high weight fraction Au (~30%) offered a unique conductive lubricant for RF MEMs switches. Introduction of nanoparticle liquids to RF MEMS contact surfaces helped: i) increase electrical conductivity between lubricated contact interfaces without organic component degradation and contact melting; ii) prevent adhesion failure of the contact by introduction of nanosized asperities. For high current (1 mA) switching, the material prevented shorting and extended lifetime by five orders of magnitude over that of self-assembled monolayer lubricants without nanoparticles. At low current, no degradation of contact resistance was observed through 106 cycles.
9:00 PM - A3.4
In-situ Electrical Characteristics Mapping of Deformed, Thin Flexible Carbon-Nanotube Electrodes
Shane Juhl 1 , Michael Arlen 1 , David Jacobs 1 , Hilmar Koerner 1 , Liming Dai 2 , Julia Hsu 3 , Richard Vaia 1 Show Abstract
1 , AFRL, Wright-Patterson AFB, Ohio, United States, 2 , Wright Brothers Institute, Dayton, Ohio, United States, 3 , Sandia National Labs, Albuquerque, New Mexico, United States
9:00 PM - A3.41
Optically Pumped Surface-Emitting Lasing using Self-Assembled Block Copolymer Distributed Bragg Reflectors.
Jongseung Yoon 1 , Wonmok Lee 1 2 , Edwin Thomas 1 Show Abstract
1 , MIT, Cambridge, Massachusetts, United States, 2 , Samsung Advanced Institute of Technology, Yongin-si, Gyeonggi-do Korea (the Republic of)
9:00 PM - A3.42
Dynamic Color Changes in Cholesteric Liquid Crystals.
Lalgudi Natarajan 2 , Vincent Tondiglia 2 , Jeremy Wofford 1 , Stephen Siwecki 2 , Richard Sutherland 2 , Eric Beckel 3 , Timothy Bunning 1 Show Abstract
2 , Science Applications International Corporation, Dayton, Ohio, United States, 1 Materials and Manufacturing Directorate, Air Force Research laboratory, Wright-Patterson AFB, Dayton, Ohio, United States, 3 , Anteon Corporation, Dayton, Ohio, United States
9:00 PM - A3.43
Synthesis and Characterization of Polyethylene-b-Poly(ethylene oxide)-b-Polyhedral Oligomeric Silsesquioxane (POSS) Triblock Oligomers
Jianjun Miao 1 , Li Cui 1 , Lei Zhu 1 Show Abstract
1 Institute of Materials Science and Department of Chemical, Materials, and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, United States
In this work, the crystallization and self-assembly behaviors of well-defined triblock oligomers polyethylene-b-poly(ethylene oxide)-b-polyhedral oligomeric silsesquioxane (POSS) (PE-b-PEO-b-POSS) were studied. The samples were characterized by differential scanning calorimetry, synchrotron small angle X-ray scattering (SAXS), and wide angle X-ray diffraction (WAXD). The orientations of PE and POSS crystals in a shear-oriented sample were determined by 2D WAXD and SAXS. The results also suggest that POSS molecules form an ABCA-stacked four-layer lamellar (trigonal) crystal sandwiched by two PE-PEO layers. The solution-cast sample shows a long period of 13.37 nm, corresponding to an extended chain conformation in the PE crystals. When grown from the melt, the d-spacing decreases to 10.13 nm, indicative of once-folded chain conformation for the PE block.
9:00 PM - A3.44
The Programmable Location of Janus Nanoparticles within Block Copolymer Domains.
Youngjong Kang 1 , Rafal Mickiewicz 1 , Vahik Krikorian 1 , Edwin Thomas 1 Show Abstract
1 ISN, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
9:00 PM - A3.45
Melting Point Measurement of Ethylene Vinyl Acetate Thin Films
Wei Liu 1 , Clive Li 1 , Xiaoting Jia 1 , Jonathan Sokolov 1 , Miriam Rafailovich 1 Show Abstract
1 , State University of New York at Stony Brook, Stony Brook, New York, United States
9:00 PM - A3.47
Molecular Simulation of the Crystal-amorphous Interphase in Semicrystalline Polypropylene.
Vikram Kuppa 1 , Gregory Rutledge 1 Show Abstract
1 Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
9:00 PM - A3.48
Two-dimensional Star-branched Polymers Grown by Diffusion.
Guillermo Ramirez-Santiago 1 , Carlos Mendoza 2 Show Abstract
1 Instituto de Fisica, Universidad Nacinal Autonoma de Mexico, Mexico, Distrito Federal, Mexico, 2 Instituto de Investigacion en Materiales, UNAM, Mexico, Distrito Federal, Mexico
9:00 PM - A3.5
Preparation and Characterization of Polyimide Coated with Cu and Ni Layers for Electromagnetic Ray Protection.
Eun Sun Ji 1 , Young Hwan Kim 1 , Young Soo Kang 1 Show Abstract
1 Chemistry, Pukyong National Univ., Pusan Korea (the Republic of)
9:00 PM - A3.50
Renewable Resources as an Alternate Feedstock for Organic Synthesis and Self-Assembled Soft Materials: A New Paradigm
George John 1 Show Abstract
1 Department of Chemistry, City College of the City University of New York, New York, New York, United States
9:00 PM - A3.51
Phase Behavior and Morphology of Immiscible Enantiomeric Polylactide Block Copolymers and Their Stereocomplexes
Lu Sun 1 , Lei Zhu 1 , Igors Sics 2 , Lixia Rong 2 , Benjamin Hsiao 2 Show Abstract
1 Institute of Materials Science and Department of Chemical, Materials, and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, United States, 2 Department of Chemistry , State University of New York at Stony Brook, Stony Brook, New York, United States
Polylactide (PLA), as an emerging thermoplastic material derived from renewable resource, has attracted considerable attention. Especially, its block copolymers have demonstrated potentials as biomedical materials. In this work, we successfully synthesized enantiomeric PLA block copolymers with narrow molecular weight distributions using AlEt3 catalyzed ring-opening polymerization of L- and D-lactides from hydroxyl-terminated hydrophilic [poly(ethylene oxide) (PEO)] and hydrophobic [poly(ethylene-co-1,2-butylene) (PEB)] oligomers. Morphology of neat PLA block copolymers was studied by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The stereocomplexes from equal molar blends of PEO-b-PLLA (2,000-5,000) and PEB-b-PDLA (4,200-5,000) were cast from chloroform. Prior to the stereocomplex formation, two different thermal treatments were performed, resulting in lamellar and cylindrical morphologies in the melt, respectively. Interestingly, on the basis of a TEM study, onion-like stereocomplex lamellar crystals were obtained due to a difference in the molecular weights of the PEO-2k and PEB-4.2k blocks. Based on the SAXS and TEM results, a tentative model was proposed to explain these onion lamellar crystals.
9:00 PM - A3.52
Synthesis and Accelerated Degradation of Tunable Biocompatible Thermoplastic Polyurethanes Containing POSS.
Pamela Knight 1 , Haihu Qin 1 , Kyungmin Lee 1 , John Bobiak 1 , Patrick Mather 1 Show Abstract
1 Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, Ohio, United States
Increasing demand in the medical field for biocompatible drug delivery systems has led to the investigation of biodegradable polymers. The hydrophilic and bioresorbable nature of polyesters has pushed them to the forefront of this technology. Unfortunately, the inherently poor mechanical properties of these polymers limit their range of applications. To overcome this, a new system is introduced which incorporates inorganic polyhedral oligosilsequioxane (POSS) into an organic poly(lactide-ran-caprolactone) backbone. These materials are formed to create a multiblock thermoplastic polyurethane (TPU) with tunable hard and soft blocks. First, the soft block is synthesized through a ring-opening polymerization of d,l-lactide and ε-caprolactone, using either a hydrophilic or hydrophobic initiator. Increasing the caprolactone content as well as using the hydrophilic initiator serves to decrease the glass transition temperature (Tg), as shown by DSC. A hard block is then added onto the material by using isobutyl-functionalized POSS diol as the chain extender and either a flexible or rigid diisocyanate. Through this method, control over the thermal and mechanical properties can be maintained. Due to thermodynamic incompatibility between the blocks, the POSS moieties will microphase segregate and form physical crosslinks through crystallization. These micro-domains can then be manipulated by changing the hard block to soft block ratio. Tg of the final material is also determined through the diisocyanate chosen. Selected TPUs, featuring systematic variation in composition as described above, were processed into films and degraded in-vitro using PBS buffer solutions at 37 °C with pH values of 4, 6, and 7.4, with the acidic media simulating the environment of foreign body giant cells involved in in-vivo degradation. Degraded samples were analyzed through changes in water absorption, mass loss, and molecular weight over time. We observed that the rate of degradation (mass loss) for the POSS-TPUs was fastest for the samples in the more acidic buffer solution. Also, films made from the hydrophilic initiator, flexible diisocyanate, and least amount of POSS diol lost mass the quickest in each experiment. Quite surprisingly, the materials appeared to be pH-responsive, exhibiting pH-dependent hydrolysis mechanisms. In particular, the films switched from being purely bulk degraders in the pH = 7.4 and 6 environments to adding a surface erosion component at the more acidic pH = 4. Evidence supporting this conclusion will be presented, including the analytical methods mentioned above and supplemented with 1H-NMR and FTIR spectroscopy.
9:00 PM - A3.53
Controlled Ordering of Nanoparticles in Ordered Copolymer Matrices.
Chieh-Tsung Lo 1 , Byeongdu Lee 1 , Pappannan Thiyagarajan 1 , Randall Winans 1 Show Abstract
1 , Argonne National Laboratory, Argonne, Illinois, United States
Self assembly of Au nanoparticles in microphase separated diblock copolymers composed of poly(styrene-b-2vinylpyridine) as functions of particle concentration and molecular weight of block copolymers was investigated using small angle X-ray scattering (SAXS) and transition electron microscopy (TEM). The addition of nanoparticles reduces the degree of segregation, inducing an order-disorder transition. This behavior is different from that with the addition of homopolymers because of the additional entropic penalty of nanoparticles to the system. When the nanoparticles are constrained in the minor domain of block copolymer they organize into 3D arrays. On the other hand, if the nanoparticles are in the major domain their distribution becomes random. In the thin film architecture, nanoparticles modify the interactions between block copolymers and the substrate, inducing a transformation from parallel 2D ordering to vertical 2D assemblies. Knowledge gained from these studies on the effects of nanoparticle loading and molecular weight of block copolymers on the phase behavior of the polymer nanocomposites will be valuable for tailoring the physical properties of these novel nanocomposites for various applications.The authors acknowledge the support from Strategic LDRD grant (2005-219-NO). This work was benefited by the use of APS and IPNS funded by DOE-BES under contract # W-31-109-ENG-38.
9:00 PM - A3.54
Self-healing Polymer Coatings.
Soo Hyoun Cho 1 3 4 , Scott White 1 2 3 , Paul Braun 1 3 4 Show Abstract
1 Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 4 Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Department of Aerospace Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Self-healing polymer coatings, at a very simplistic level, mimic the self-healing nature of skin in living systems. In our presentation, we will demonstrate a new paradigm for self-healing polymer coatings which provides very good corrosion resistance to metal substrates, even after deep scratch damage. Previously, we demonstrated the excellent self-healing properties of a chemically stable polymer composite based on the tin-catalyzed polycondensation of phase-separated droplets containing hydroxyl end-functionalized polydimethylsiloxane (HOPDMS) and polydiethoxysiloxane (PDES).1 However, an even more important application of this self-healing system is for coatings. Polymer coatings are commonly applied to metal substrates to prevent corrosion in aggressive environments such as high humidity and under salt water. Once the polymer coating has been breached, for example due to cracking or scratches, it loses its effectiveness, and corrosion can rapidly propagate across the substrate. The self-healing system we will describe prevents corrosion by healing the damage through a healing reaction triggered by the actual damage event. The anti-corrosion properties of the self-healing polymer on metal substrates are investigated by corrosion resistance and electrochemical tests. Even after scratch damage completely through the substrate, the coating is able to heal, while control samples which do not include all the necessary healing components reveal rapid corrosion propagation. This self-healing coating solution can be easily applied to most substrate materials, and is compatible with most common polymer matrices. Self-healing coatings have the potential to extend the life time of coatings and can dramatically reduce the frequency of repair.1. Cho, S. H., Andersson, H. M., White, S. R., Sottos, N. R., and Braun, P. V. Polydimethylsiloxane-based self-healing materials. Adv. Mater. 18, 997-1000 (2006).
9:00 PM - A3.55
Synthetic Antimicrobial Oligomers Induce Composition-dependent Topological Transition in Membranes.
Lihua Yang 1 , Abhijit Mishra 1 , Kirstin Purdy 1 , Abhigyan Som 4 , Gregory Tew 4 , Gerard C.L. Wong 1 2 3 Show Abstract
1 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 4 Polymer Science & Engineering, University of Massachusetts at Amherst, Amherst, Massachusetts, United States, 2 Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 Bioengineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
9:00 PM - A3.56
Selective Surface Modification of Poly-(N-isopropylacrylamide) Gel by a Surface Imprinting Method.
Akiyuki Ueda 1 , Yukikazu Takeoka 1 , Takahiro Seki 1 Show Abstract
1 , Graduate School of Engineering Nagoya University, Nagoya Japan
In recent years, the study of the surface properties of gels have become the focus of much interest due to their function similarity to living body and biocompatibility. So it is necessary to develop a method of chemical surface modification to control the surface properties of gels. In this study, we obtained poly-N-isopropylacrylamide (PNIPA) gel surface modified with sulfonic acid group by a surface imprinting method. We fabricated the patterning of sulfonic acid groups on the surface of PNIPA gel by a surface imprinting method as following procedures: 1) amino-terminated SAMs was formed onto a silicon substrate. 2) UV light was irradiated on an amino-terminated SAMs through a photomask. 3) a vinyl monomer having sulfonic acid group was electrostatically coupled with the amino group of the SAMs. 4) A gel is prepared on the vinyl monomer modified silicon substrate by free-radical polymerization. We attempted the adsorption test of amino-group modified fluorescence microbeads onto the surface of the gel. These results indicate that the surface modified gel membrane with sulfonic acid can be fabricated from this surface molecularly imprinting method. Furthermore we are planning on observing the surface state of the gel by a contact angle measurement, XPS.
9:00 PM - A3.57
Structure Formation in Multilayerd Films Prepared by the Layer-by-Layer Deposition Using PAA and HM-PEO.
Jin Hwa Seo 1 , Jodie Lutkenhaus 2 , Junoh Kim 1 , JongChoo Lim 3 , Paula Hammond 2 , Kookheon Char 1 Show Abstract
1 School of Chemical and Biological Engineering, Seoul National University, Seoul Korea (the Republic of), 2 Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Department of Chemical and Biological Engineering, Dongguk University, Seoul Korea (the Republic of)
The layer-by-layer (LbL) assembly is a well-established technique to prepare thin and versatile multilayered films based on various intermolecular interactions between pairing polymers. Thin and highly tunable platform can thus be easily achieved by the LbL assembly. In present study, poly(acrylic acid) (PAA) and hydrophobically modified poly(ethylene oxide) (HM-PEO) multilayers based on the hydrogen bonding between the component polymer pair have been prepared by the LbL deposition method. Dip assembled HM-PEO/PAA multilayers yield unique film morphologies in comparison with PEO/PAA multilayers due to the micellar formation of HM-PEO owing to the hydrophobic attraction between alkyl chains end-capped with the PEO chains. Individual HM-PEO micelles were connected through the bridging PEO chains to form temporary networks on multilayer surface and induced peculiar surface morphology on HM-PEO/PAA multilayers above the critical number of bilayers. These were studied with optical microscope as well as fluorescence microscope with pyrene dyes that allows us to monitor the sites of HM-PEO micelles. It is also noted that the film morphology can also be controlled by changing the solvent polarity. By adding alcohol into water, the water polarity decreases and the hydrophobic association between alkyl chains is effectively suppressed, yield the disappearance of such unique surface structures. In addition to the solvent effect, the surface structure was also shown to be tunable with temperature, molecular weight of HM-PEO and the assembly method. Free-standing multilayered HM-PEO/PAA thin films can also be obtained, which allow us to characterize the composition and physical properties of such thin polymer multilayers in more detail. It is noted that the introduction of hydrophobic moieties in the multilayers facilitates the peel-off from many different types of substrates, yielding free-standing multilayers. Because HM-PEO has hydrophobic moieties which reduce the adsorption energy between multilayer and substrate, free-standing HM-PEO/PAA multilayers were obtained by direct peel-off from different substrates. Their composition and thermal properties were also obtained using TGA and DSC measurements.
9:00 PM - A3.58
Dispersion of Single Walled Carbon Nanotubes by Self Assembly of Polymers
Ramasudhakar Dhullipudi 1 , Tabbetha Dobbins 1 2 , Yuri Lvov 1 Show Abstract
1 Institute for Micromanufacturing, Louisiana Tech University, Ruston, Louisiana, United States, 2 Dept. of Physics, Grambling State University, Grambling, Louisiana, United States
Dispersion and solubility of single walled nanotubes (SWNT) is one of the inhibiting factors affecting their tailorability for different electronic, chemical and mechanical applications. Employing layer-by-layer self assembly technique for functionalization of SWNTs with polyelectrolytes resulted in their dispersion. This functionalization increases their adaptability for nanocomposite film formation. Results of functionalization of SWNTs with different polyelectrolytes and their characterization with atomic force microscopy (AFM), UV-Vis spectroscopy, and transmission electron microscopy (TEM) will be discussed. Nanocomposite nanotube films formed with the dispersed SWNTs using various deposition techniques were used and the effect of dispersion on the film morphology was analyzed.
9:00 PM - A3.59
Thickness Measurement of Langmuir-Blodgett Films of Vinylidene Fluoride-Trifluoroethylene Copolymers with X-ray Reflectivity.
Jihee Kim 1 , Shireen Adenwalla 1 , Stephen Ducharme 1 Show Abstract
1 Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska, United States
Nanometer thickness scale control is one of the advantages of ferroelectric polymer films made by Langmuir-Blodgett (LB) deposition technique, compared to the conventional techniques, such as solvent spin coating and casting. Therefore, measuring the thickness per transfer is crucial to show the excellent layering properties of the samples as well as for further nanoscale studies.In this study samples with thickness less than 50 nm were investigated with x-ray. The x-ray reflectivity (XRR) technique, a very powerful tool to measure the thickness of thin films with atomic scale accuracy over large areas, therefore, has been extensively used for soft matter studies, such as thin films of liquids and polymers. We measured the thicknesses of a series of LB films of P(VDF-TrFE 70:30) and P(VDF-TrFE 50:50) and determined the average thickness per transfer, 2.6 ± 0.2 nm and 2.3 ± 0.2 nm, respectively, which means that 1 LB transfer consists of approximately 6 molecular layers. This study revealed the impressive nanometer scale layering property of films in a relatively large lateral scale of 54 mm2.This work is supported by the Nebraska Research Initiative and the National Science Foundation.
9:00 PM - A3.6
Deformation-Conductivity-Structure Relationship of Polyurethane Elastomer / Carbon Nanofiber Composites.
Michael Arlen 1 , Barney Taylor 2 , Hilmar Koerner 2 , Richard Vaia 1 Show Abstract
1 MLBP, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio, United States, 2 , Universal Technology Corporation, Beavercreek, Ohio, United States
Physical characteristics such as the electrical conductivity of polymers containing dispersions of nanofibers are anticipated to be anisotropic and sensitive to deformation due to the extreme anisotropy of the nanofibers. For example the DC conductivity, σDC, of solution cast composites consisting of semicrystalline polyurethane (PU) and vapor grown multiwall carbon nanofibers (CNF) exhibit up to 3 orders of magnitude difference in σDC parallel and perpendicular to the surface. The percolation threshold occurred at 0.6 vol% CNF which is significantly lower compared to the 18 vol% carbon black (CB) required for electrical percolation in the same polymer matrix. The in-plane piezoresistive coefficient at low strains (ε<0.10) is positive and decreases with increasing filler loading, which is thought to reflect the increased number of low resistance conducting pathways. The robustness of the conductive network was better for the CNF composites compared to CB composites, which is attributed to the high aspect ratio nature of the CNF. Compared to pure PU, the CNF-PU composite exhibits greater mechanical hysteresis during initial cyclic deformation up to ε~0.3. In situ WAXS monitoring during the tensile elongation reveals the CNFs are initially isotropic in the sample plane and orient slightly in the strain direction, but upon relaxation do not fully reorient. In contrast, residual orientation of pre-existing crystallites after deformation is greater for pure PU than the CNF-PU composites. These results imply that the permanent deformation of the CNFs or CNF-network structure contributes to the permanent electrical hysteresis of the sample. Also for the CNF-PU composite, the extent of hysteresis in the mechanical and electrical response with repeated deformation cycles becomes reproducible after five cycles. These results demonstrate the advantages of using high aspect ratio conductive fillers in piezoresistive materials and the influence of the Payne effect on the electrical properties.
9:00 PM - A3.60
Chlorophyll-a self-assembly: A Low Temperature STM Investigation.
Violeta Iancu 1 , Saw Hla 1 Show Abstract
1 Physics and Astronomy, Ohio University, Athens, Ohio, United States
9:00 PM - A3.61
Hydrodynamic Boundary Conditions at a Polymer Interface.
Laurence Lurio 1 , Xuesong Hu 2 , Zhang Jiang 3 , Suresh Naryanan 2 , Xuesong Jiao 2 , Alec Sandy 2 , Sunil Sinha 3 , Jyotsana Lal 2 Show Abstract
1 Department of Physics, Northern Illinois University, Dekalb, Illinois, United States, 2 , Argonne National Laboratory, Argonne, Illinois, United States, 3 Department of physics, University of California San Diego, La Jolla, California, United States
9:00 PM - A3.62
Tuning of Surface Properties through Site-Selective Deposition of Nanoparticles and Subsequent Place-Exchange Reactions.
Hao Xu 1 , Rui Hong 2 , Roy Shenhar 3 , Tongxiang Lu 1 , Oktay Uzun 4 , Vincent Rotello 1 Show Abstract
1 Chemistry, Umass-Amherst, Amherst, Massachusetts, United States, 2 , Harvard University, Cambridge, Massachusetts, United States, 3 , The Hebrew University of Jerusalem, Jerusalem Israel, 4 , MIT, Cambridge, Massachusetts, United States
Utilization of ultra-thin grafted films to impart desired chemical/physical properties onto solid substrates has become a powerful technique to prepare new composite and functional materials. Engineered microscopic surface structures to present specific functionalities with controlled surface densities within well-defined regions are crucial for integrated devices and fabrication processes. Here we present a versatile strategy of tailoring local properties of patterned surfaces by site-selective immobilization of functionalized nanoparticles and subsequent place-exchange reactions. Metallic and semiconductor nanoparticles are among the most versatile building blocks employed in the creation of nanoscale materials. They present unique optical, magnetic and electronic properties due to their high surface areas and the confinement of electronic states. We will demonstrate the selective deposition of chemically monolayer-functionalized nanoparticles (e.g. Au, CdSe, CdSe/ZnS) onto various solid substrates (e.g. silicon, glass, quartz, plastics) prepatterned through photolithography or diblock copolymer templated self-assembly. The interactions responsible for the immobilization include electrostatics, hydrogen bonding or simple hydrophobic interactions. The modified surfaces display respective optical properties or (semi)conductivity provided by nanoparticles, regardless of the underlying substrates used. The resulted surface properties can be further tuned by incubating into desired thiol solutions. The excess free thiol molecules in solution are place exchanged onto surface-immobilized nanoparticles, which induce the change of surface properties significantly. The wettability (i.e. hydrophobicity / hydrophilicity), biocompatibility (i.e. resistance to nonspecific protein adsorption and cell attachment), and conductivity of surfaces can be conveniently manipulated in this approach. This methodology provides a practical tool for applications in microelectronics and medial devices.
9:00 PM - A3.63
New Self-Assemblies of Catalytic Nanowires in Large Scales.
Z. Ryan Tian 1 2 3 , Wenjun Dong 1 , Michelle McDonald 1 , Michael Jackson 1 , Andrew Cogbill 1 , Feng Chen 1 , Carmen Padilla 2 Show Abstract
1 Chemistry/Biochemistry, University of Arkansas, Fayetteville, Arkansas, United States, 2 Cell and Molecular Biology, University of ARkansas, Fayetteville, Arkansas, United States, 3 Microelectronics and Photonics, University of ARkansas, Fayetteville, Arkansas, United States
9:00 PM - A3.65
High-Density Microbubble Formation by Utilizing the Specific Additives for Chemical-less Degreasing Process.
Makoto Miyamoto 1 , Shin-Ichiro Kuroki 2 , Koji Kotani 2 , Satoshi Ueyama 1 , Junji Hirotsuji 1 , Takashi Ito 2 Show Abstract
1 Environmental Technology & Systems , Mitsubishi Electric Corporation, Amagasaki Japan, 2 Electronics Engineering, Tohoku University, Sendai Japan
It is increasingly required to reduce the environmental impacts and costs in the field of industrial cleaning. The authors focused on the large surface area and the adsorption capability of the microbubble for degreasing process. In order to treat large amounts of grease within a short time, it is important to generate microbubbles as high-density (many microbubbles per unit water volume) as possible for reducing cleaning time. We confirmed that the specific alcohol compound of several tens to several hundreds parts per million (ppm) were effective to prevent the merging of bubbles. It has not been so clear how the trace amount of additive actually works although it has been proven effective. We tested the microbubble formation for several kinds of alcohol compound with similar structures (structural isomers) and found they were considerably different in their capability to generate microbubbles. That effect is considered that the alcohol molecules are adsorbed onto the microbubble surface and thereby electrical double layer forms on their surfaces. We assumed the capacitor model of the microbubble crowd and measured dielectric constants of microbubble crowd which were generated by adding several alcohol compounds in an originally designed cell. It was confirmed that the correlation between the dielectric constants and the bubble diameters. The mechanism will be discussed in detail in the current presentation.
9:00 PM - A3.66
Preparation and Optical Properties of Ordered Arrays of Glucose-Responsible Submicrogel Particles Trapped in Inverse Opal.
Masaki Honda 1 , Yukikazu Takeoka 1 , Takahiro Seki 1 , Kazunori Kataoka 2 Show Abstract
1 Engineering, Graduate School of Engineering Nagoya University, Nagoya Japan, 2 Engineering, The University of Tokyo Graduate School of Engineering , Tokyo Japan
First, we obtained a closest-packing photonic crystal that act as a photonic crystal composed of monodisperse silica particles 300 nm in diameter. A styrene monomer containing an initiator was infiltrated into the crystal and was polymerized so as to trap the cystalline structure. The composite film was soaked in HF solution to remove the silica particles completely. Then the resulting inverse opal polystyrene film with interconnecting porous structure could serve as a template to obtain glucose-responsible nanogel particles. We found that the intensity of Bragg diffraction is altered by the existence of glucose due to the swelling of the embedded nanogel particles. Such behavior was dependent on the glucose concentration.
9:00 PM - A3.67
Phase Behavior and Morphological Characteristics of Block Copolymer Nanocomposites.
Michelle Bowman 1 , Jon Samseth 2 , Kell Mortensen 6 , Steve Smith 3 , Michael Bockstaller 5 , Richard Spontak 4 1 Show Abstract
1 Materials Science & Engineering, North Carolina State University, Cary, North Carolina, United States, 2 Materials & Chemistry, SINTEF, Trondheim Norway, 6 , Riso National Laboratory, Roskilde Denmark, 3 Chemical Technology, Proctor & Gamble, Cincinnati, Ohio, United States, 5 Materials Science & Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 4 Chemical & Biomolecular Engineering, North Carolilna State University, Raleigh, North Carolina, United States
9:00 PM - A3.68
Luminescent Nanocrystal Modified Photoresin for Fabrication of High-aspect Ratio Three-dimensional Microstructures.
Chiara Ingrosso 1 2 , Vahid Fakhfouri 3 , Maria Lucia Curri 1 , Marinella Striccoli 1 , Angela Agostiano 1 2 , Juergen Brugger 3 , Gabi Gruetzner 4 , Anja Voigt 4 Show Abstract
1 IPCF, CNR , Bari Italy, 2 Chemistry, University of Bari, Bari Italy, 3 Microsystems Laboratory, EPFL, Lausanne Switzerland, 4 Microresist Technology, GmbH, Berlin Germany
9:00 PM - A3.69
Modulation of Optical and Magnetic Properties in Nanocomposites through Controlled Particle Spacing.
Sudhanshu Srivastava 1 , Ayush Verma 1 , Benjamin Frankamp 1 , Vincent Rotello 1 Show Abstract
1 , UMASS-Amherst, Amherst, Massachusetts, United States
9:00 PM - A3.7
Lamellar to Inverted Hexagonal Phase Transition in DNA Complexes with Calamitic, Discotic, and Cubic Shaped Cationic Lipids
Li Cui 1 , Lei Zhu 1 Show Abstract
1 Institute of Materials Science and Department of Chemical, Materials, and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, United States
In this study, we report the lipid tail molecular shape/size effect on the mesophase self-assembly of various cationic lipids complexed with double-stranded DNA. The molecular shape of the cationic lipids was tailored from rodlike (a cyanobiphenyl imidazolium salt) to discotic (a triphenylene imidazolium salt), and finally to cubic [a polyhedral oligomeric silsesquioxane (POSS) imidazolium salt]. An increase in the cross-sectional area of the hydrophobic tails with respect to the hydrophilic imidazolium head induced a negative spontaneous curvature of the cationic lipids. As a result, a morphological change from lamello-columnar phase for the DNA-cyanobiphenyl imidazolium salt (DNA-rod) and DNA-triphenylene imidazolium salt (DNA-disk) complexes to an inverted hexagonal phase for the DNA-POSS imidazolium salt (DNA-cube) complex was observed. The DNA-rod complex had a typical smectic A (SmA) lamellar morphology, while the DNA-disk complex had a double lamello-columnar phase. However, when the lipid tail changed to POSS, an inverted hexagonal morphology was achieved.
9:00 PM - A3.70
Carbon Nanotube Micro Optical Grippers.
Shaoxin Lu 1 , Balaji Panchapakesan 1 Show Abstract
1 Dept. of Electrical Engineering, University of Delaware, Newark, Delaware, United States
9:00 PM - A3.71
Synthesis and Characterizaion of Thermoreversible Hydrogels from Associating Polymers.
Jun Jiang 1 , Chunhua Li 1 , Michael Rubinstein 2 , Ralph Colby 3 , Jack Lombardi 4 , Daniel Cohn 5 , Miriam Rafailovich 1 , Jonathan Sokolov 1 Show Abstract
1 , State University of New York at Stony Brook, Stony Brook, New York, United States, 2 Department of Chemistry , University of North Carolina at Chapel Hill, Chapel Hill, New York, United States, 3 Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 4 , Estee Lauder Company, Melville, New York, United States, 5 , Hebrew University, Jerusalem Israel
9:00 PM - A3.72
Effect of Solvent Concentration to the Preparation of Polystyrene Nanoparticles Using Polyelectrolyte Block Copolymer.
Edwin Garcia 1 , Young Choi 1 , Hyoung Moon 1 , Bumsuk Jung 1 Show Abstract
1 Department of Environmental Engineering and Biotechnology, Myongji University, Yongin City Korea (the Republic of)
9:00 PM - A3.73
Multi-Layered Polymer Nanoparticles with a Calcium Phosphate Core.
Janine Schwiertz 1 , Wolfgang Meyer-Zaika 1 , Matthias Epple 1 Show Abstract
1 Institute of Inorganic Chemistry, University of Duisburg-Essen, Essen Germany
9:00 PM - A3.8
Immobilization and in-plane Alignment of Columnar Assemblies of Lyotropic Liquid Crystals in Liquid Crystals/silica Hybrid Films.
Mitsuo Hara 1 , Norihiro Mizoshita 1 , Shusaku Nagano 1 , Takahiro Seki 1 Show Abstract
1 , Graduate School of Engineering, Nagoya University, Nagoya Japan
9:00 PM - A3.9
Deformation of Vesicles in Shear Flow.
William Uspal 1 , Kurt Smith 1 , Anna Balazs 1 Show Abstract
1 Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Understanding the behavior of cells and vesicles in driven flows is crucial to nano- and microfluidic technologies. We model the behavior of single component and multi-component budded amphiphilic bilayer vesicles in simple shear using dissipative particle dynamics. Deformation of floppy and tense single component vesicles in shear is quantitatively characterized. We find that deformation of tense vesicles is linear with capillary number, and that deformation of floppy vesicles is piecewise linear with two segments corresponding to availability and exhaustion of the reservoir of area in the floppy membrane. Morphological change of multicomponent budded vesicles in shear is investigated and two major vesicle transformation processes are observed: 1.) Migration of the bud to the vesicle tip, followed by pinch-off and formation of a daughter vesicle, and 2.) flattening of the bud into a circular domain and circulation around the vesicle. The phase diagram is mapped out in the region of interest, and the pathway of evolution of the neck morphology during shear-driven pinch-off is closely examined. Potential biomimetic applications in drug delivery and controlled release are discussed.
Richard A. Vaia Air Force Research Laboratory
Jan Genzer North Carolina State University
Gareth H. McKinley Massachusetts Institute of Technology
Nelson Tabiryan Beam Engineering for Advanced Measurements Company
A4: Reversible Motion
Tuesday AM, November 28, 2006
Room 203 (Hynes)
9:00 AM - **A4.1
Soft Responsive Matter for Robotic Applications.
Christopher Rahn 1 Show Abstract
1 Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States
9:30 AM - **A4.2
Active Nanotube-based Polymer Composites: Towards a Tailored Electromechanical Response.
Zoubeida Ounaies 1 Show Abstract
1 Aerospace department, Texas A&M University, College Station, Texas, United States
The mechanical, electrical, and thermal properties exhibited by carbon nanotubes provide strong motivation for their use as inclusions in polymers, potentially resulting in composites that combine structural functions with sensing and actuation capabilities. In this work, recent results regarding carbon nanotube (CNT)-polymer composites are introduced. Stable solutions of CNT combined with a series of polymers, ranging from non-polar to highly polar, are prepared and processed into various forms such as thick and thin films, and fibers. Physical properties of the nanocomposites are assessed as a function of nanoinclusion concentration and degree of dispersion and orientation. The interaction between the nanoinclusion and the polymer matrix is studied with spectrometry, x-ray diffraction and microscopy. Electrical, dielectric and mechanical properties of the reinforced composites are also measured. The focus of the study is three-fold: (1) investigate the interaction between the nanoinclusion and the dipole group in the polymer by evaluating percolation of nanoinclusion-polymer systems and identifying local field enhancement and other electric field-driven interactions; (2) study the resulting macroscale performance by processing and characterizing random and electric field-oriented composites; and (3) explore the resulting phenomenological responses by developing a theoretical understanding that relates inclusion network and polymer morphology to structural and sensing/actuation properties. It is found that the nanoinclusions increase the dielectric, electrical, mechanical and thermal properties of the polymer. A notable finding is that addition of CNTs in non-polar to weakly polar polymers creates an electromechanical coupling, along with improved structural reinforcement, rendering the composite multifunctional. The observed electromechanical coupling is measured above the percolation threshold where the composite behaves as a conductor. The actuation response is electrostriction, and increases with increase in CNT concentration up to 1vol%. Above this value a slight decrease is observed in the strain indicating a plateau in the behavior. In the case of highly polar polymers, such as b-CN APB/ODPA and PVDF, presence of CNTs increases the piezoelectric strain response, and decreases actuation voltage by one to two orders of magnitudes. These investigations promise to increase our understanding of the mechanisms involved, particularly as related to nanoparticle/polymer interaction. This in turn would allow us to tailor the composites--by modifying dipole moiety, CNT content, and CNT distribution--to yield desired performance in terms of electromechanical conversion, actuation voltage, electroactive strain, and response time. A fundamental understanding of interfacial interactions between nanoinclusions and polymer matrices would constitute a major leap toward the development of polymer nanocomposites optimized for a functional performance.
10:00 AM - A4.3
Liquid Crystal Elastomers: Finite Element Simulation and Applications
Robin Selinger 1 , Badel Mbanga 1 , Jonathan Selinger 1 Show Abstract
1 Chemical Physics, Kent State University, Kent, Ohio, United States
The burgeoning field of liquid crystal elastomer research offers great promise for a variety of engineering applications, where these materials serve as soft actuators triggered by changes of temperature, electric field, illumination, or chemical environment. Heretofore, theorists have focused on elucidating the fundamental microscopic theory of these materials. To go beyond this microscopic view, e.g. to enable design and testing of prototype devices made from nematic elastomers, we have developed a novel finite element algorithm that models macroscopic shape change in these materials. Because the operation of such devices involves large strains and rotations, our algorithm accounts for the effects of nonlinear elasticity, and our explicit dynamics procedure conserves energy and momentum to high precision. The algorithm also accounts for heterogeneous boundary conditions and nonuniform stimuli, and can describe samples of arbitrary initial shape defined by an unstructured mesh. Prototype devices we have tested hitherto include pumps, active membranes, self-propelled locomotion, and orientation controllers, where in each case the device’s function is driven by the mechanical response of an assembly of soft actuators. Through this research effort we hope to bridge the gap between fundamental microscopic theory and practical engineering design.
10:15 AM - A4.4
Morphology and Deformation Induced Ordering of Side Chain Liquid Crystalline Block Copolymers: For use in Electromechanical Applications.
Eric Verploegen 1 , Paula Hammond 2 , Lu Tian 2 Show Abstract
1 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, 2 Chemical Engineering, MIT, Cambridge, Massachusetts, United States
Liquid crystalline (LC) polymer research has gained interest due to the usefulness of liquid crystals in many applications other than displays. Some of these applications include memory devices, sensors, and variable light valves. Small molecules liquid crystals are commonly used in display applications due to the fast response time that these materials can achieve. However, there are many advantages to using block copolymers in these applications, such as surface stabilization caused by the block copolymer morphology, as well as improved mechanical properties.This research seeks to examine the potential use of ferroelectric LC block copolymer elastomers as actuators. These devices can be used as artificial muscles, in microrobotics, in micromachinery, in MEMS, and in other applications that require gates or valves. The proposed polymers for this research offer unique processing, mechanical, and electrical advantages over the current technologies because self assembly under optimized conditions lead to thermoplastic elastomers. To this end, a series of well defined smectic side chain liquid crystalline (LC) block copolymers with a low Tg siloxane center block has been synthesized via anionic polymerization. The presence of a smectic liquid crystalline phase and the block copolymer mesophase are observed across various temperature ranges. The influence of mechanical deformation upon the morphologies of the liquid crystalline and block copolymer mesophases was investigated. The interactions between the smectic LC and the block copolymer morphologies and their influence upon their respective orientations in response to shear fields are detailed. Additionally, it was found that various modifications to the liquid crystalline moiety could significantly influence the clearing points for the smectic liquid crystalline phase, as well as significantly influencing the nanophase segregation of the block copolymer.Optimized oscillatory shear conditions yielded samples displaying a nearly uniform morphology across the thickness of the film, which is essential for enabling the use of these materials for electromechanical applications. The liquid crystals were chosen such that the smectic C* phase will be present at the desired operating temperature and electromechanical actuation can be obtained.
10:30 AM - A4.5
Actuatable Membranes Based on Polypyrrole-Coated Vertically Aligned Carbon Nanofibers.
Benjamin Fletcher 1 2 , Scott Retterer 1 5 , Timothy McKnight 1 3 , Anatoli Melechko 1 4 , Jason Fowlkes 1 2 , Michael Simpson 1 2 4 , Mitchel Doktycz 5 Show Abstract
1 Molecular Scale Engineering and Nanoscale Technology Research Group, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, 5 Biological and Nanoscale Systems Group, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Monolithic Systems Group, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 Center for Nanophase Materials Science, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
11:15 AM - **A4.6
New Designs for Molecular Actuation.
Timothy Swager 1 Show Abstract
1 , MIT, Cambridge, Massachusetts, United States
This lecture will discuss the design of molecules and materials for the formation of polymer actuators. Systems containing hinge structures will be presented and the unique complexities associated with achieving bulk actuation from this structural class will be discussed. Additional molecular systems that transform from non-planar kinked structures to planar units and electroactive polymers based upon these materials will be described. Achieving polymer actuators with performance required for most applications will require a variety of properties that are not achievable in a single material. Materials integration into complex actuation systems is necessary to achieve suitable performance metrics and systems containing single wall carbon nanotubes will be discussed.
11:45 AM - **A4.7
From Electrical to Fuel Powered Artificial Muscles
Von Ebron 1 , Zhiwei Yang 1 , Daniel Seyer 1 , Mikhail Kozlov 1 , Jiyoung Oh 1 2 , Hui Xie 1 , Joselito Razal 1 , John Ferraris 1 , Alan MacDiarmid 1 , Ray Baughman 1 Show Abstract
1 Department of Chemistry and The NanoTech Institute, University of Texas at Dallas, Richardson, Texas, United States, 2 Research Center of Dielectric & Advanced Matter Physics and Department of Physics, Pusan National University, Busan Korea (the Republic of)
We here experimentally demonstrate artificial muscles that convert the energy of a high-energy-density fuel to mechanical energy. These muscles are fuel cells that in some embodiments store electrical charge and use changes in stored charge for mechanical actuation. The highest demonstrated actuator generated strains and mechanical output power densities are comparable to natural skeletal muscle, and the actuator generated stresses are over a hundred times higher than for natural skeletal muscle. Since the energy density of fuels like methanol is ∼30 times higher than for advanced Li batteries, this advance seems quite important for such applications as autonomous robots or prosthetic limbs, where long operation without recharging or refueling is needed.
12:15 PM - A4.8
Photo-patternable Liquid Crystal Actuators with High Strain and Work Density Through Optimization of Molecular Configuration.
Casper van Oosten 1 , Kenneth Harris 1 , Cees Bastiaansen 1 , Dirk Broer 2 Show Abstract
1 Polymer Technology, Eindhoven University of Technology, Eindhoven Netherlands, 2 , Philips Research Laboratories, Eindhoven Netherlands
12:30 PM - A4.9
Azo Liquid Crystal ``Shape Memory" Polymer and its Photoactuation in Evanescent Light.
U. Hrozhyk 1 , S. Serak 1 , N. Tabiryan 1 , Timothy Bunning 2 Show Abstract
1 , Beam Engineering for Advanced Measurements Corporation, Winter Park, Florida, United States, 2 , Air Force Research Laboratory, WPAFB, Ohio, United States
12:45 PM - A4.10
Photoregulation of Ions/Molecules Transport through Synthetic Channels of Photoresponsive Azobenzene-modified Nanoporous Membrane.
Zhu Chen 1 , Nanguo Liu 2 , Darren Dunphy 3 , David Adams 3 , C. Brinker 1 3 Show Abstract
1 , University of New Mexico, Albuquerque, New Mexico, United States, 2 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 , Sandia national Laboratory, Albuquerque, New Mexico, United States
A5: Dynamic Surfaces I
Tuesday PM, November 28, 2006
Room 203 (Hynes)
2:30 PM - **A5.1
Selective Self-assembly of Nanoparticles on Adaptive Nanopillar Arrays.
Shu Yang 1 Show Abstract
1 Materials Science and Engineering, University of Pennsylvania, Philadelphia, New Jersey, United States
Control of interfacial properties, such as wettability, adhesion, and friction, is important for both fundamental science and practical applications. The ability to independently vary the chemical and physical heterogeneities on a topographically structured surface may provide unprecedented control of molecular recognition and reorganization. Using microcontact printing and surface-initiated atom transfer radical polymerization (ATRP), we have selectively grafted a thin layer of thermoresponsive poly(N-isopropylacrylamide) (PNIPA) brushes onto different locations, everywhere vs. the tips of the nanopillar arrays. The surface wettability can be dynamically tuned from highly hydrophobic to superhyhydrophilic (brushes grafted everywhere) or moderately hydrophobic state (brushes only on tips) depending on the grafting location and brush density. On such “smart” surface, we show promise to spatially control the self-assembly of nanoparticles (both hydrophobic and hydrophilic) either on the tips or everywhere in response to a small temperature change..
3:00 PM - A5.2
Amphiphilic Graft Copolymers for Nanofiltration Membranes with Tunable Pore Size
Ayse Asatekin 1 , Anne Mayes 1 Show Abstract
1 Material Science and Engineering, MIT, Cambridge, Massachusetts, United States
Different separations often require membranes of different pore sizes. Therefore, membranes whose pore sizes can be changed easily by changing simple process parameters are highly desirable, making the membrane material useful for a variety of applications at lower cost. However, high flux and fouling resistance properties must not be sacrificed for this end. Studies on such membranes are especially rare in the nanofiltration (NF) field. To address these issues, the amphiphilic graft copolymers, poly(vinylidene fluoride)-graft-poly(oxyethylene) methacrylate (PVDF-g-POEM) and polyacrylonitrile-graft-poly(ethylene glycol) (PAN-g-PEG), were synthesized and used in the fabrication of thin film composite nanofiltration (NF) membranes. These membranes were prepared by coating commercial ultrafiltration membranes by a thin film of graft copolymer. Upon microphase separation of backbone and side-chains, hydrophilic “nanochannels” are created that allow water passage. The size of the nanochannels depends on the size scale of phase separation, and therefore can be tuned using processing parameters that influence the phase separation and chain conformation either during membrane coating (e.g. non-solvent bath) or during the filtration operation (e.g. solvent quality of POEM, temperature, pressure, ionic strength), making it possible to choose the size cut-off using a single the membrane. Flux, size selectivity and the fouling resistance were tested using dead-end filtration cells. Pore size was characterized by the filtration of rigid dye molecules as probes. The ability of the membranes to fractionate at different size scales was investigated through its ability to separate three antibiotics using the same membrane at two different conditions. In addition to tunable pore sizes, the membranes displayed fluxes higher than commercial nanofiltration membranes and high fouling resistance.
3:15 PM - A5.3
``Nanonails" – a Simple Geometrical Approach to ``Superlyophobic" Surfaces.
Tom Krupenkin 1 , Amir Ahuja 1 , Ashley Taylor 1 , Alex Sidorenko 1 , Todd Salamon 1 , Edgar Labaton 1 Show Abstract
1 , Bell Labs, Lucent Technologies, Murray Hill, New Jersey, United States
3:30 PM - A5.4
Reversible Conversion of Conducting Polymer Films from Superhydrophobic to Superhydrophilic.
Lianbin Xu 1 , Wilfred Chen 1 , Ashok Mulchandani 1 , Yushan Yan 1 Show Abstract
1 Department of Chemical and Environmental Engineering, University of California at Riverside, Riverside, California, United States
4:15 PM - **A5.5
Synthesis of Responsive Polymer Films via Macromolecular Anchoring Layer.
Igor Luzinov 1 Show Abstract
1 School of Materials S&E, Clemson University, Clemson, South Carolina, United States
Responsive surfaces can be described as surfaces that have the ability to respond in a controllable fashion to specific environmental stimuli. In the present communication, we describe synthesis of the responsive polymer films via macromolecular anchoring layer. Namely, the polymers constituting the films were grafted to the surface through ultrathin reactive poly(glycidyl methacrylate) layer. The responsive heterogeneous grafted layers were synthesized by “grafting to” approach, “grafting from” approach, and their combination. The morphology and surface chemical composition of the responsive films were investigated using scanning probe microscopy and contact angle measurements. The films demonstrated pronounced tendencies to phase segregation. Rinsing the synthesized grafted layers in selective solvents and observing the change in water contact angle as a function of the grafted layer composition studied the switching nature of the surface.
4:45 PM - **A5.6
Conformational Mechanics of Stimulus-Responsive Polypeptides on Surfaces.
Stefan Zauscher 1 2 Show Abstract
1 Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina, United States, 2 Center for Biologically Inspired Materials and Materials Science, Duke University, Durham, North Carolina, United States
The design and fabrication of surfaces with patterned, conformationally switchable biopolymeric structures is important for sensing and actuation applications on the micro and nanoscales. We recently demonstrated that stimulus-responsive, elastin-like polypeptides (ELPs) and their hierarchical assemblies on surfaces show great promise for actuation, sensing, and biotechnological applications. ELPs offer a tunable means to transduce and amplify changes in the solvent environment, such as changes in pH, temperature, or ionic strength by a large change in their molecular conformation and surface energy. While interfacial applications of ELPs have been prototypically demonstrated, a systematic investigation of the conformational mechanics at the solid-liquid interface is lacking. We will present results from experiments ranging from the ensemble to the single molecule level that employ and explore the conformational and surface energetic behavior of surface-grafted ELPs. We show that hydrophobic interactions between ELPs grafted to a surface and ELPs free in solution are responsible for their reversible association above the lower critical solution temperature. Furthermore, we show results from force-spectroscopy measurements on the single molecule level that suggest that ELPs are well described by a random coil polymer model, without significant secondary structure and, importantly, that force spectroscopy is able to distinguish differences in the hydrophobic hydration of single ELP molecules. Our results contribute significantly to the understanding of the conformational and mechanical consequences of an environmentally triggered phase transition in stimulus-responsive macromolecules.
5:15 PM - A5.7
Thermally-Responsive Polymer-co-Peptide Brushes for Bio-separation and Sensing Surfaces: Tuning Peptide-Mediated Mineralization and Nanoparticle Binding Strength via Functional Group Display.
Steve Diamanti 1 2 , Shafi Arifuzzaman 3 , Theresa Foley 4 , Mark Pender 1 , Joseph Slocik 1 2 , Jan Genzer 3 , Evangelos Manias 4 , Rajesh Naik 1 , Richard Vaia 1 Show Abstract
1 , Air Force Research Laboratories, Wright-Patterson AFB, Ohio, United States, 2 , National Research Council, Washington , District of Columbia, United States, 3 , North Carolina State University, Raleigh-Durham, North Carolina, United States, 4 , Pennsylvania State University, University Park, Pennsylvania, United States
The design of an inexpensive, simple, and robust biosensor platform that can be tuned to separate and/or respond to many different biological species would be of tremendous use for military, homeland security, and medical diagnostic applications. One major challenge is to minimize reagents and maximize read-out response. Pervious efforts have demonstrated that gradient surfaces of thermally-responsive poly(N-isopropyl acrylamide) PNIPAAm and poly(hydroxyethyl methacrylate) PHEMA, brushes spatially localize biomolecule absorption, while minimizing non-specific adsorption of the same biomolecule on other regions of the gradient. To further improve the specificity as well as to provide embedded (latent) functionality for reflective read-out of the binding events, post-polymerization modification of the brushes with peptides identified by phage display is discussed. Using standard succinimide-based coupling, hydroxyl pendants of PHEMA and PNIPAAm-b-PHEMA brushes were post-synthetically conjugated to oligo-peptides as well as long-chain alkanes and oligo(ethylene glycols) through an alpha-terminus primary amine. Film thickness (ellipsometry) and surface energy (contact angle) correspondingly increased after functionalization. XPS depth profiling indicated that coupling preferentially occurred at the solution-polymer interface with efficiencies ranging from 10-40%. Generally, peptides (GGAYSSGAFPPMPPFGG and MHGKTQATSGTIQS) identified as having gold mineralization activity enhance the mineralization at the conjugate brush surface, whereas non-polar functionalities, such as hexadecane, drastically decrease surface activity. The surface mineralization behavior of trityrosine, a simple peptide analog known to have gold reduction ability, was found to have similar mineralization ability as the much more complex phage display analogs. Irrespective of peptide composition, the buffer conditions were found to have the biggest impact on the overall surface activity, where standard HEPES buffer participates in the Au(III) reduction and reduces any specificity that may occur at the peptide-conjugated brush surface. Overall, due to the generality of the conjugation chemistry, numerous chemical functionalities can be post-synthetically incorporated, which will modify the ability of the thermally-responsive polymer gradient to mineralize inorganics, adsorb nanoparticles, or bind biomolecules. Additionally, comparison of the mineralization activity from the surface-bound peptides in various buffers to those free in solution helps to elucidate the role of secondary structure and local environment on the peptide-mediated biomineralization process.
5:30 PM - A5.8
Peptide-Modified Responsive Surfaces with Built-in Logic.
Ryan Toomey 1 , Lawrence Neuman 1 , Ajay Vidyasagar 1 , Peng Tian 1 Show Abstract
1 Chemical Engineering, University of South Florida, Tampa, Florida, United States
5:45 PM - A5.9
Protein Adsorption Amplification at the Macromolecular Stimulus-Responsive Transition
Miao Ye 1 , Christine Ortiz 1 Show Abstract
1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Surfaces capable of reversibly and dynamically controlling protein adsorption in response to changes in their surrounding environment is key to a variety of applications like biosensors, microfluidic bioanalytical devices and directed cellular function. Recently, we prepared stimulus responsive surfaces via chemically end-attached "brush-brushes" formed by chemisorption of mono(end)-functional thiol-terminated poly(methacrylic acid-g-ethylene glycol) (HS-poly(MAA-g-EG)) with three different macromolecular architectures (number average molecular weight, Mn= 27K, PEG graft density, PEG(%)= 7.7%, backbone contour length, Lcontour= 41.1 nm; Mn= 15K, PEG(%)= 8.8%, Lcontour= 22.1 nm; Mn= 17K, PEG(%)= 1.9%, Lcontour= 39.8 nm). The higher PEG grafting density surfaces (27K, 15K) exhibited the unique property of "nanomechanical switching" with pH, i.e. the normal intersurface force inverted from net repulsive (high pH, ionized uncomplexed side chains) to net attractive (low pH, side-chain/main-chain hydrogen bonding complexation). The 17K polymer brushes did not exhibit nanomechanical switching and maintained a slightly repulsive intersurface force at low pH. Surface plasmon resonance (SPR) was employed to assess the adsorption of human serum albumin (HSA) to these poly(MAA-g-EG) brushes at the concentration of 1 mg/ml in aqueous buffer solutions of varying pH and a constant ionic strength of 0.005M (flow rate = 2 μl/min, flow time = 30 minutes, 25 C°). All surfaces exhibited pH-responsive protein adsorption, for example the 27K polymer demonstrated a dramatic drop in the amount of adsorbed protein from ~ 3.76 ng/mm2 at pH9 to ~ 0.07 ng/mm2 at pH4. Polymers with a higher grafting density of hydrophilic PEG side chains and longer polymer backbones showed relatively much less HSA adsorption at high pH, but increased more protein adsorption at low pH. Surprisingly, HSA adsorption was found to be greatly amplified at intermediate pH6 (~1.4-1.8 × greater than that of the hydrophobic state of polymer layers at pH4). Higher PEG grafting density and a longer polymer backbone demonstrated larger protein adsorption amplification at pH6, which may be due to increased molecular mobility/disorder at the conformational transition. Since the conformational information at nanometer scale can not be probed from a nanomechanical experiment. The hypothesis of a unique, perpendicular to the substrate, “rod-like” conformation of polymer brushes at the transition stage (pH6) with kinetically favorable “channels” or “pores” for HSA globules diffusion needs to be further investigated. Contrary to the prediction of gradual change of pH-responsive protein adsorption, our results suggest that the most dramatic change of a stimulus responsive polymer surface could occur at a metastable state.