Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session A4: Responsive and Adaptable Polymeric Materials |
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Sponsoring Units: DPOLY DMP GSNP Chair: Timothy Bunning, Air Force Research Laboratory Room: Colorado Convention Center Korbel 2B-3B |
Monday, March 5, 2007 8:00AM - 8:36AM |
A4.00001: Adaptive and Responsive Polymer NanoComposites Invited Speaker: In addition to thermal-mechanical improvements of commodity plastics, polymer nanocomposite concepts offer opportunities to impart \textit{responsive} characteristics as well as enhance the performance of \textit{active} polymers, including shape memory and piezo - resistivity. Opportunities arise from 1) the utilization of the extensive polymer-nanoparticle interfacial area ($>$500 m$^{2}$/g), 2) the responsiveness of the percolative network of the nanoparticle to external fields, and 3) the impact of nanoscale compositional fluctuations on the local electric field. As an example, carbon nanotube addition to shape memory polymers increases blocking stress by 100{\%} and provides novel electrical and optical methods to trigger recovery. Similarly, the pyro-resitive character of carbon nanotube -- polyimide nanocomposites depends on the surface modification of the nanotube, displaying a positive coefficient of resistivity (resistance increase with temperature) from cryogenic to the glass transition temperature. Challenges facing characterization and the establishment of structure-property correlations will be discussed. [Preview Abstract] |
Monday, March 5, 2007 8:36AM - 9:12AM |
A4.00002: Hydrophobic Hydration of Stimulus-Responsive Polyproteins Measured by Single Molecule Force Spectroscopy Invited Speaker: We present a new procedure to reduce and analyze force-extension data obtained by single molecule force spectroscopy (SMFS). This approach allows, for the first time, to infer effects of solvent quality and minor changes in molecular architecture on molecular-elasticity of individual (bio)macromolecules. Specifically, we show how changes in the effective Kuhn segment length can be used to interpret the hydrophobic hydration behavior of elastin-like polypeptides (ELPs).Our results are intriguing as they suggest that SMFS in combination with our analysis procedure can be used to study the subtleties of polypeptide-water interactions on the single molecule level. We also report on the force-induced cis-trans isomerization of prolines, which are repeated every fifth residue in the main chain of ELPs. We present evidence for this mechanism by Monte Carlo simulations of the force-extension curves using an elastically coupled two-state system. Our results suggest that SMFS could be used to assay proline cis-trans isomerization in proteins and may thus have significant potential diagnostic utility. [Preview Abstract] |
Monday, March 5, 2007 9:12AM - 9:48AM |
A4.00003: Nature's Mechanisms for Tough, Self-healing Polymers and Polymer Adhesives Invited Speaker: Spider silk$^{2}$ and the natural polymer adhesives in abalone shells$^{3}$ and bone$^{4,5}$ can give us insights into nature's mechanisms for tough, self-healing polymers and polymer adhesives. The natural polymer adhesives in biomaterials have been optimized by evolution. An optimized polymer adhesive has five characteristics. 1) It holds together the strong elements of the composite. 2) It yields just before the strong elements would otherwise break. 3) It dissipates large amounts of energy as it yields. 4) It self heals after it yields. 5) It takes just a few percent by weight. Both natural polymer adhesives and silk rely on sacrificial bonds and hidden length for toughness and self-healing.$^{6}$ A relatively large energy, of order 100eV, is required to stretch a polymer molecule after a weak bond, a sacrificial bond, breaks and liberates hidden length, which was previously hidden, typically in a loop or folded domain, from whatever was stretching the polymer. The bond is called sacrificial if it breaks at forces well below the forces that could otherwise break the polymer backbone, typically greater than 1nN. In many biological cases, the breaking of sacrificial bonds has been found to be reversible, thereby also providing a ``self-healing'' property to the material.$^{2-4}$ Individual polymer adhesive molecules based on sacrificial bonds and hidden length can supply forces of order 300pN over distances of 100s of nanometers. Model calculations show that a few percent by weight of adhesives based on these principles could be optimized adhesives for high performance composite materials including nanotube and graphene sheet composites. \newline \newline $^{2}$N. Becker, E. Oroudjev, S. Mutz et al., Nature Materials \textbf{2} (4), 278 (2003). \newline $^{3}$B. L. Smith, T. E. Schaffer, M. Viani et al., Nature \textbf{399} (6738), 761 (1999). \newline $^{4}$J. B. Thompson, J. H. Kindt, B. Drake et al., Nature \textbf{414} (6865), 773 (2001). \newline $^{5}$G. E. Fantner, T. Hassenkam, J. H. Kindt et al., Nature Materials \textbf{4}, 612 (2005). \newline $^{6}$G. E. Fantner, E. Oroudjev, G. Schitter et al., Biophysical Journal \textbf{90} (4), 1411 (2006). [Preview Abstract] |
Monday, March 5, 2007 9:48AM - 10:24AM |
A4.00004: Cell microrheology in health and disease" be suitable for your session Invited Speaker: |
Monday, March 5, 2007 10:24AM - 11:00AM |
A4.00005: Is experimental heteropolymer sequence design practical, or does it belong to the realm of science fiction? Invited Speaker: In the protein folding context, theorists consider various methods of sequence design, which turns out a very useful way to look at various heteropolymer properties. Simultaneously and largely independently, there is a rather old idea to find an experimental counterpart of computational and theoretical sequence design algorithms. Here, we review some of the experiments in this direction along with some of the more recent theoretical advances and come to the guarded conclusion that full experimental realization of sequence design is possible but probably remote. [Preview Abstract] |
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