Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session J42: Padden Award Symposium |
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Sponsoring Units: DPOLY Chair: John Torkelson, Northwestern University Room: A302/303 |
Tuesday, March 22, 2011 11:15AM - 11:27AM |
J42.00001: Directing crystallization of organic semiconductors around corners in solution-processed thin films Stephanie S. Lee, Samuel Tang, Marsha Loth, John E. Anthony, Detlef-M. Smilgies, Arthur Woll, Yueh-Lin Loo We demonstrate the ability to pre-specify the crystallization direction of triethylsilylethynyl anthradithiophene (TES ADT), an organic semiconductor, in solution-processed thin films. Manipulating the substrate surface energy allows us to control the crystallization rate of TES ADT, which ranges from 9 to 25 $\mu $m/s, during solvent-vapor annealing. Grazing-incidence x-ray diffraction experiments on as-spun TES ADT films indicate that the initial in-plane orientation of TES ADT is influenced by the surface energy of the underlying substrate, likely due to the competition between strong molecule-molecule interactions and its wettability on the substrate. By imposing surface energy specific patterns on the substrate prior to the deposition of TES ADT, we can preferentially direct TES ADT crystallization around bends and sharp corners to form channels with high hole mobility for charge transport. [Preview Abstract] |
Tuesday, March 22, 2011 11:27AM - 11:39AM |
J42.00002: Solid-State Structure and Crystallization in Double-Crystalline Diblock Copolymers Sheng Li, Sasha Myers, Richard Register Crystalline-crystalline block copolymers, containing two or more chemically distinct crystallizable blocks, can potentially exhibit a rich array of complex solid-state structures. Double-crystalline diblock copolymers of linear polyethylene (LPE) and hydrogenated polynorbornene (hPN) were synthesized, and their crystallization behavior and morphology were examined using two-dimensional simultaneous time-resolved synchrotron small-angle and wide-angle x-ray scattering. Previously, we showed that in symmetric diblock copolymers of hPN and LPE, with molecular weights above 50 kg/mol, the hPN block crystallizes first and sets the solid-state microstructure. In the present work, we extend these studies to lower molecular weights, and more importantly, we examine the structural relationship between the crystals formed by the two blocks under different conditions of confinement. When the diblock molecular weight is reduced to 20 kg/mol, the LPE block crystallizes first, even when LPE is the minority component, and restricts hPN to crystallize between the LPE lamellae. Furthermore, in both the high and low molecular weight diblock copolymers, the second-to-crystallize block always orients its crystals orthogonally to the first-to-crystallize block. [Preview Abstract] |
Tuesday, March 22, 2011 11:39AM - 11:51AM |
J42.00003: Electric Field Induced Ordering of a Battery Electrolyte Scott Mullin, Nitash Balsara A disordered mixture of a symmetric poly(styrene-\textit{block}-ethylene oxide) (SEO) copolymer and lithium bis(trifluoromethanesulfonimide) (a lithium salt) was placed between two lithium metal electrodes. Application of a 3V potential across the electrodes results in a current density of 15 mA/cm$^{2}$ and order formation as evidenced by the instantaneous development of a sharp small-angle X-ray scattering (SAXS) ring and Bragg spots due to the presence of a few large coherent grains. With time, radial streaks emanated from the ring, leading to a scattering pattern that resembles a sun dial. Our preliminary hypothesis is that these streaks are due to salt concentration gradients that occur when the current is passed. This gradient results in coherent grains within which the domain size changes continuously. To our knowledge, this kind of structure has not been observed previously in block copolymers. The disordered phase is recovered in the bulk when the applied potential is turned off, and the open circuit voltage of the cell and the SAXS invariant relax with similar time constants. This work represents the first step toward designing responsive battery electrolytes wherein structure and ion transport depends on the state-of-charge of the battery. [Preview Abstract] |
Tuesday, March 22, 2011 11:51AM - 12:03PM |
J42.00004: Gradient Solvent Vapor Annealing of Thin Films Julie Albert, Timothy Bogart, Ronald Lewis, Thomas Epps The development of block copolymer materials for emerging nanotechnologies requires an understanding of how surface energy/chemistry and annealing conditions affect thin film self-assembly. Specifically, in solvent vapor annealing (SVA), the use of solvent mixtures and the manipulation of solvent vapor concentration are promising approaches for obtaining a desired morphology or nanostructure orientation. We designed and fabricated solvent-resistant devices to produce discrete SVA gradients in composition and/or concentration to efficiently explore SVA parameter space. We annealed copolymer films containing poly(styrene), poly(isoprene), and/or poly(methyl methacrylate) blocks, monitored film thicknesses during annealing, and characterized film morphologies with atomic force microscopy. Morphological changes across the gradients such as the transformation from parallel cylinders to spheres with increasing solvent selectivity provided insight into thin film self-assembly, and the gradient device has enabled us to determine transition compositions and/or concentrations. [Preview Abstract] |
Tuesday, March 22, 2011 12:03PM - 12:15PM |
J42.00005: Injectable solid peptide hydrogel: shear-thinning and instant recovery Congqi Yan, Joel Schneider, Darrin Pochan Peptides were designed to fold into $\beta $-hairpins once exposed to physiological conditions and consequently self-assemble into rigid hydrogel. The network consists of branched and entangled 3nm-wide fibrils. These physical gels shear thin and flow under a proper shear stress but immediately recover back into solids on removal of stress with further rigidity restoring over time. To elucidate mechanisms of these physical properties, gel behavior during and after flow was investigated. Gel stiffness recovered immediately after shear, as well as gel stiffening over time post-recovery, were found dependent on shear rate and shear duration. From scattering measurements during flow, the gel network structure was observed unchanged from the static state at all shear rates investigated. Thus, the peptide gel networks fracture into gel domains ($>$200nm as determined by scattering) during shear thinning/flow but can instantly percolate back into a solid hydrogel after cessation of shear, stiffening further as particle boundaries relax. As these gels are essentially the same solid material, before and after shear, they offer great potential as well-defined, injectable carriers of biomedical therapies where a desired encapsulated therapeutic payload is delivered to an \textit{in vivo} site by simple syringe injection. [Preview Abstract] |
Tuesday, March 22, 2011 12:15PM - 12:27PM |
J42.00006: Transport properties of mechanically deformed polymer networks Hassan Masoud, Alexander Alexeev We develop a hybrid computational method to probe how the permeation and hindered diffusion change when an isotropic polymer network is deformed by an externally applied force. We use a bond-bending lattice spring model to capture the micromechanics of random networks of interconnected elastic filaments coupled with the dissipative particle dynamics to explicitly model the viscous fluid and diffusive solutes. Our simulations reveal that the network transport properties are defined by the network porosity and by the degree of network anisotropy due to network mechanical deformations. We also show that the internal network structure does not affect the permeation and diffusion of stressed and unstressed networks. Furthermore, our results indicate that permeability of mechanically deformed networks can be predicted based on the alignment of network filaments that is characterized by a second order orientation tensor. Our findings have implications for designing drug delivery agents, tissue engineering, and understanding the function of certain biological systems. [Preview Abstract] |
Tuesday, March 22, 2011 12:27PM - 12:39PM |
J42.00007: Numerical coarse-graining of polymer field theories Michael Villet, Glenn Fredrickson Field theoretic models of polymers are widely used to investigate polymer self-assembly, but numerical simulations of these models that include full fluctuation physics are computationally demanding and infrequently conducted. To enable efficient multi-scale simulations, we propose the use of systematically coarse-grained field theories that can be simulated on coarse computational lattices while accurately incorporating the effects of important sub-lattice-scale physics. We present a rigorous formalism for generating such coarse-grained theories from data obtained from small-scale fine-grained simulations, and demonstrate our methodology's effectiveness for a representative polymer solution model. [Preview Abstract] |
Tuesday, March 22, 2011 12:39PM - 12:51PM |
J42.00008: Molecular mobility and cation conduction in sulfonated polyester copolymer ionomers Gregory Tudryn, Daniel King, Michael O'Reilly, Karen Winey, Ralph Colby Poly(ethylene oxide) ionomers are candidate materials for electrolytes in energy storage devices due to the ability of ether oxygen to solvate cations. Copolyester ionomers are synthesized via condensation of sulfonated phthalates with mixtures of PEG and PTMG to make random copolymer ionomers with identical ion content. Variation of the PEG/PTMG composition changes Tg, dielectric constant and ionic aggregation; each with consequences for ion transport. Dielectric spectroscopy is used to determine number density of conducting ions, their mobility and extent of aggregation. Conductivity and mobility show Vogel temperature dependence and increase with PEG content; even though PTMG ionomers have lower Tg. Conducting ion densities show Arrhenius temperature dependence and are nearly identical for polymers containing PEG. SAXS confirms the extent of aggregation and temperature response from dielectric results, and exposes phase separation as PTMG content is increased. The tradeoff between ion-solvation and low Tg in this study provides fundamental understanding of ionic aggregation and ion transport in polymer electrolytes. [Preview Abstract] |
Tuesday, March 22, 2011 12:51PM - 1:03PM |
J42.00009: Strain Localization and Sliding Friction in Physically Associating Networks Kendra A. Erk, Kenneth R. Shull Experimental evidence, constitutive models, and scaling law arguments are presented for shear-induced strain localization in triblock copolymer gels deformed at reduced rates spanning almost four orders of magnitude. Strain-stiffening behavior proceeded by rapid softening is believed to result from the formation of highly localized regions of deformation in the macromolecular network. This behavior is described by a constitutive model that incorporates the strain energy and relaxation of individual strands in the network. Flow curves predicted from the model are non-monotonic, consistent with the onset of flow instabilities at high shear rates. Connections are established between the stress response of the gel at large strain and traditional sliding friction experiments of gelatin gels on glass. The gel's well-defined network structure and tunable range of relaxation times allow for these gels to be useful model systems for future studies of flow instabilities in physically associating solutions. [Preview Abstract] |
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