Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session J18: Frank J. Padden Award Symposium |
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Sponsoring Units: DPOLY Chair: Russell Composto, University of Pennsylvania Room: Morial Convention Center 210 |
Tuesday, March 11, 2008 11:15AM - 11:27AM |
J18.00001: Use DNA solutions to model polymer entanglement in flow: simultaneous rheometric and particle-tracking velocimetric measurements Pouyan Boukany, Shi-Qing Wang Entangled aqueous DNA solutions are ideal as a model system to examine nonlinear flow features including stress overshoot in startup shear and shear thinning phenomenon. These soft systems can be strongly entangled with 60 entanglement points per chain and a terminal relaxation time as long as 1000~s at 1 {\%} concentration [1-2]. They allow a comparison between the steady state attained with a startup shear and that attained through an ``infinitely'' slow ramping up of the applied shear rate. Indeed, startup shear in the nonlinear (stress plateau) region causes the DNA solutions to yield inhomogeneously, resulting in permanent shear banding. However, the slowly ramped-up shear into the same final rate as applied in startup shear allowed the solutions to avoid shear inhomogeneity. Thus, we demonstrated that it is possible for the final steady states to be different depending on how an entangled system is brought into the same final experimental condition. This result implies that it is ill-defined to pursue conventional constitutive relationship in flow of entangled polymers. \newline [1] Boukany, P. E.; Hu, T. H.; Wang, S. Q. textit{Macromolecules} 2007, under review. [2] Boukany, P. E.; Wang, S. Q. \textit{J. Rheol}. 2007, under review. [Preview Abstract] |
Tuesday, March 11, 2008 11:27AM - 11:39AM |
J18.00002: Membrane-Enhanced Surface Acoustic Wave Analysis of Polymer Brushes David A. Brass, Kenneth R. Shull We show that detailed structural information about polymer brushes can be obtained from a simple membrane inflation technique in conjunction with a quartz crystal resonator. The sensitivity of these quartz crystal resonators is determined by the propagation of acoustic shear waves through the materials that are placed in contact with the oscillating crystal. Coupling of the these 'surface acoustic waves' into the membrane is strongly affected by the thickness of the brush layer, which is in turn affected by specific interactions between the polymer brush and the surface with which it is brought into contact. The mechanical resonance of the quartz crystal is affected by these brush parameters, and we refer to the accompanying analysis of this resonance as 'membrane-enhanced surface acoustic wave analysis'. The analysis combines self consistent mean field theory of the polymer brush with the relevant theories of acoustic wave propagation. The model has been tested experimentally with grafted poly(ethylene glycol) brushes in contact with thermoplastic elastomer membranes. We also show how the technique can be used to quantify the strength of specific interactions between the electrode surface of the quartz resonator and functional groups placed at the ends of the PEG brushes. [Preview Abstract] |
Tuesday, March 11, 2008 11:39AM - 11:51AM |
J18.00003: Advances in Organic Single-Crystal Transistors Alejandro L. Briseno, Zhenan Bao, Younan Xia, Samson A. Jenekhe Organic semiconductors, including conjugated small molecules and polymers, constitute next-generation materials for displays, circuits, and a vast array of other electronic applications. The performances of organic single-crystal transistors have recently surpassed the performance levels of amorphous silicon devices. Despite the high mobilities of single-crystal devices, there are many factors limiting their applications. Currently, single crystals are handpicked and made into an individual device. Another challenge is to achieve control of crystallinity in polymer nanostructures. There is a need to explore nanowires as solution-processable materials because of the cost-effective aspect in fabricating devices. Therefore, in order to meet the requirements for fabricating practical devices, we have resolved the aforementioned issues by patterning organic single-crystal transistors and polymers. We have developed solution-phase methods for preparing organic single-crystal nanowires from p- and n-type semiconductors and highly oriented nanowires from polymer semiconductors. Furthermore, we have realized high-performance transistors and demonstrated the first all-polymer complementary circuit. [Preview Abstract] |
Tuesday, March 11, 2008 11:51AM - 12:03PM |
J18.00004: Effect of lithium ion distribution on conductivity of block copolymer electrolytes Enrique Gomez, Nitash Balsara Energy-filtered transmission electron microscopy (EFTEM) was used to determine the distribution of lithium ions in mixtures of bis(trifluoromethane)sulfonimide lithium salt and symmetric poly(styrene-\textit{block}-ethylene oxide) copolymers (PS-PEO). EFTEM results show that the salt is increasingly localized to the middle of the PEO lamellae as the molecular weight of the copolymers is increased. Computer simulations by Borodin and Smith (Macromolecules, 1998, 31, 8396) demonstrate that coordination between lithium ions and PEO chains is diminished for chains that are stretched. Local stretching in block copolymers is modeled using self-consistent field theory (SCFT). Good agreement between EFTEM and SCFT is obtained by postulating a linear relationship between local chain stretching and lithium ion concentration. AC impedance spectroscopy experiments show an increase in the conductivity of PS-PEO/salt mixtures with increasing molecular weight of PS-PEO. The EFTEM/SCFT results suggest that the increase in ionic conductivity with increasing molecular weight is due to segregation of the lithium salt away from PS/PEO interfaces where segmental motion is retarded due to connectivity to slow-moving PS chains. These results may aid in developing all-solid state rechargeable lithium batteries with PS-PEO serving as a dry electrolyte. [Preview Abstract] |
Tuesday, March 11, 2008 12:03PM - 12:15PM |
J18.00005: Self-assembly of metal--polymer analogues of amphiphilic triblock copolymers Zhihong Nie, Daniele Fava, Eugenia Kumacheva, Shan Zou, Gilbert Walker, Michael Rubinstein We proposed a block copolymer approach to the self-assembly of inorganic nanrods terminated with polymer molecules at both ends. We organized metal nanorods in structures with varying geometries by using a striking analogy between amphiphilic ABA triblock copolymers and the hydrophilic nanorods tetheredwith hydrophobic polymer chains at both ends. The self-assembly was tunable and reversible and it was achieved solely by changing the solvent quality for the constituent blocks. The distance between adjacent nanorods along chains can be tuned by varying the composition of mixture solvents or the molecular weight of polymer blocks, which allows us precisely control the plasmonic band of self-assembled structures. A systematic study of the self-assembly as a function of solvent composition and the molecular weight of the polymer blocks allowed us to construct a diagram that maps the assembled structures. This approach provides a new route to the organization of anisotropic nanoparticles by using the strategies that are established for the self-assembly of block copolymers. [Preview Abstract] |
Tuesday, March 11, 2008 12:15PM - 12:27PM |
J18.00006: Rod-Coil Block Copolymer Self-Assembly in Thin Films B.D. Olsen, V. Ganesan, R.A. Segalman The phase behavior of rod-coil block copolymers differs from that of traditional block copolymers due to the interplay between liquid crystallinity of the rod blocks and microphase separation of the rods and coils. A universal phase diagram for rod-coil diblock copolymers is prepared using experimental measurements of both the rod aligning interaction and the rod-coil repulsive interaction to transform the temperature-dependent phase transitions of a model-rod coil system into dimensionless parameter space. The rod aligning interaction, parameterized by the Maier-Saupe parameter, may be estimated from the dependence of the nematic-isotropic transition temperature on the molecular weight of the rod homopolymer. The rod-coil interaction, parameterized by the Flory-Huggins parameter, is calculated from the temperature-dependent interfacial segregation of block copolymer to a rod/coil homopolymer interface. The Flory-Huggins parameter is extracted by using it as a fitting parameter in self-consistent field theory to match simulated block copolymer surface excesses to experimental values. [Preview Abstract] |
Tuesday, March 11, 2008 12:27PM - 12:39PM |
J18.00007: Why nanoconfinement may lead to the development of polymer glasses that do not physically age Rodney Priestley, Linda Broadbelt, John Torkelson With the advent of nanotechnology, polymers will be used at increasingly smaller length scales, $i.e$., the nanoscale. Recently, it has been shown that nanoconfined polymers can exhibit astounding changes in glassy-state properties relative to bulk. Physical aging, $i.e$., the change in properties as a function of annealing time below the glass transition temperature, determines the end-use properties of polymer glasses. How nanoconfinement impacts aging has emerged as a key technological and scientific question. Conventional techniques for monitoring aging of bulk polymers are incapable of doing so for nanoconfined polymers. Here, we present work in which we have developed fluorescence methods to monitor aging in thin polymer films. More importantly, our technique allows for the monitoring of aging at specific locations in films near interfaces. Our work indicates that nanoconfinement and interfacial effects strongly alter aging and that the development of polymer glasses that do not physically age may be possible. [Preview Abstract] |
Tuesday, March 11, 2008 12:39PM - 12:51PM |
J18.00008: Ionic Complexation Enhanced Block Copolymer Alignment with an Electric Field Jia-Yu Wang, Thomas P. Russell Alignment of microdomains in block copolymer (BCP) films by an electric field offers the possibility of fabricating ordered nanostructures that are use as templates, scaffolds and masks. In polystyrene-\textit{block}-poly(methyl methacrylate) (PS-$b$-PMMA) copolymer films, the formation of lithium-PMMA complexes, as a result of the added lithium salts, markedly enhanced the alignment of BCP microdomains under an electric field, due to the increased dielectric contrast and the weakened surface interactions which reduced the critical field strength. The formation of lithium-PMMA complexes also increases the segmental interaction, $\chi _{eff,}$ between PS and PMMA blocks with lithium-PMMA complexes, evidenced by a disorder-to-order transition (DOT) and an order-to-order transition (OOT) from spheres to cylinders. The increased $\chi _{eff}$ drove the system into a stronger phase separation, leading to a transition in the reorientation mechanism of lamellar microdomains from a disruption and re-formation to a grain rotation mediated by movement of defects. The formation of large grains amplified the ability of the electric field to overcome the interfacial interactions and eliminate defects. Consequently, the complete alignment of BCP microdomains can be achieved. [Preview Abstract] |
Tuesday, March 11, 2008 12:51PM - 1:03PM |
J18.00009: Polymer Surface Diffusion as a Function of Molecular Weight Janet Wong, Steve Granick This talk describes the first measurements to elucidate polymer surface diffusion over the full range of surface concentration and as a function of molecular weight. The model system, polystyrene adsorbed onto mica and quartz from chloroform, was selected to allow molecular weight (M) to vary by more than 2 orders of magnitude and the surface coverage to vary by more than 3 orders of magnitude. Spatially-resolved measurements of surface translational diffusion (D$_{s})$ were made using fluorescence correlation spectroscopy (FCS), which is a single-molecule technique. The value of D$_{s}$ was found to scale as a power-law in M. Remarkably, the absolute value of the power-law was -1 for mica and the most homogeneous quartz surfaces, -3/2 for less homogeneous quartz surfaces, and never took intermediate values. Explanations remain speculative but appear to involve the dominance of Rouse and reptation diffusion mechanisms, respectively. In the latter case, curvilinar motion is guided not by entanglement with other chains but instead by patchiness (topographical and chemical) of the surface adsorption sites. [Preview Abstract] |
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