Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session L17: Rheology, Transport, and Processing |
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Sponsoring Units: DPOLY Chair: Erik Hobbie, National Institute of Standards and Technology Room: Colorado Convention Center 102 |
Tuesday, March 6, 2007 2:30PM - 3:06PM |
L17.00001: BREAK
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Tuesday, March 6, 2007 3:06PM - 3:18PM |
L17.00002: A new molecular theory beyond tube model to describe cohesive breakdown in nonlinear flow of entangled polymers. Shi-Qing Wang When an entangled polymer is subjected to shear or extensional flow at a rate of deformation (RD) much greater than its dominant relaxation rate (dRR), it may not flow homogenously all the way to the limiting strain of (RD/dRR) before it suffers cohesive failure. What keeps the chains entangled is an essential question to answer before an appropriate theory of polymer flow can be established. Unlike the tube model that assumes presence of an infinitely high energy barrier preventing escape of chain entanglement, our theory [1] recognizes a finite barrier height given by kT(M/Me) for a polymer whose number of entanglements per chain is (M/Me). A second essential ingredient is to realize that a sufficiently high level of elastic force can be generated per chain by the externally imposed flow. This elastic force can overcome the entanglement (cohesive) force as a rate-activation process, leading to the onset condition for the cohesive breakup either during flow or upon cessation of flow. Flow produces frictional inter-chain interactions among all entangling chains. These interactions also resist constitutive disintegration, delaying the onset of cohesive collapse to a larger strain. A higher level of cohesive strength results from the very flow deformation that could eventually produce enough internal (elastic) forces to destroy the cohesive structure made of chain entanglement. [1] \textit{Phys. Rev. Lett. }\textbf{97}, 187801 (2006). [Preview Abstract] |
Tuesday, March 6, 2007 3:18PM - 3:30PM |
L17.00003: Image Correlation Spectroscopy of Actin Networks Jeffrey Urbach, Dan Sisan We analyze fluctuations of entangled and cross-linked networks of fluorescently-labeled actin filaments using fourier space image correlation spectroscopy. Images from a fast confocal microscope are fourier-transformed, and the autocorrelation function for each wave vector is separately computed, producing the equivalent of the intermediate scattering function. We find that for entangled networks the long time decay of the long wavelenth modes is diffusive, possibly due to to filament reptation, but that the short-time behavior is more complicated [Preview Abstract] |
Tuesday, March 6, 2007 3:30PM - 3:42PM |
L17.00004: Shape instabilities in absorbed polymer condensates Gerald Pereira Self-assembly in polymeric liquids results in morphological structures which show ordering on a range of length scales. Two examples of this phenomena are the structures which result from a homopolymer in a poor solvent and a polyelectrolyte in a poor solvent. We specifically consider the scenario of imaging such condensates via techniques such as Atomic Force Microscopy or Surface Force Apparatus, where the condensate strongly absorbs to the surface. We demonstrate that the real-space, Self-Consistent Field method is an ideal numerical tool in predicting equilibrium morphologies. New structures are predicted, which are supported by explicit free energy calculations. [Preview Abstract] |
Tuesday, March 6, 2007 3:42PM - 3:54PM |
L17.00005: ABSTRACT WITHDRAWN |
Tuesday, March 6, 2007 3:54PM - 4:06PM |
L17.00006: Large-scale diffusion in thick photopolymer systems Matthew W. Grabowski, Amy C. Sullivan, Robert R. McLeod The development of index change in millimeter-thick photopolymers designed for holography and optical devices has been studied on the micron scale using Bragg diffraction. These studies have revealed the importance of the relative diffusion rate of small molecules to the local polymerization rate but are limited to scales of less than about one micron. To probe the role of diffusion on larger scales, we introduce a form of direct-write lithography using multiple mutually-incoherent foci. This enables measurement of the development and relaxation time-constants over millimeter scales. These large-scale diffusion currents will impact applications in optical data storage, integrated optics, lenslet arrays and other large-scale exposures of these diffusion-limited photopolymers. [Preview Abstract] |
Tuesday, March 6, 2007 4:06PM - 4:18PM |
L17.00007: Mechanisms for achieving high energy density in PVDF: a first-principles investigation V. Ranjan, L. Yu, Marco Buongiorno Nardelli, J. Bernholc It is known that copolymers of vinylidene fluoride (VDF) with about 50 -- 80 {\%} VDF fraction favor the polar $\beta $-phase, and these copolymers exhibit a paraelectric phase transition below the melting point. However, a larger concentration of VDF prefers a non-polar $\alpha $-phase. We have used first-principles calculations to determine the stable phases of chloro-tri-fluoroethylene (CTFE)-VDF mixtures. Our results show that a phase transition occurs in this system as a function of the electric field, leading to a very high energy density in P(VDF-CTFE)-based capacitors. Our results for polarization, dielectric constant, and energy density are in excellent agreement with earlier experiments [1] and provide a microscopic explanation for the formation of high energy density phases in P(VDF---CTFE) and similar polymer mixtures. [1] B. Chu et al., Science 313, 334 (2006). [Preview Abstract] |
Tuesday, March 6, 2007 4:18PM - 4:30PM |
L17.00008: Interfacial Density Profiles of Poly(methyl Methacrylate) with Liquids Keiji Tanaka, Yoshihisa Fujii, Hironori Atarashi, Masahiro Hino, Toshihiko Nagamura Density profiles of a perdeuterated poly(methyl methacrylate) (dPMMA) film in water and hexane, which were `non-solvents' for dPMMA, along the direction normal to the interface were examined by neutron reflectivity. Interfaces of dPMMA with liquids were diffused in comparison with the dPMMA/air interface; the interfacial width with water was thicker than that with hexane. Interestingly, in water, the dPMMA film was composed of the strongly swollen layer and the interior region, which also contained water, in addition to the diffused layer. In contrast, such a strongly swollen layer was not observed at all in hexane. [Preview Abstract] |
Tuesday, March 6, 2007 4:30PM - 4:42PM |
L17.00009: Initiated Chemical Vapor Deposition of Poly(methyl methacrylate) Xichong Chen, Mitchell Anthamatten We are exploring a way to process Poly(methyl methacrylate) into thin films using initiated Chemical Vapor Deposition (iCVD) technique. A unique iCVD reactor was designed and several experimental parameters such as substrate temperature, hot-zone temperature, monomer/initiator molar ratio, hot-zone/substrate distance and reactor pressure were adjusted to achieve micron-thick, uniform films. Resulting films were investigated by GPC, optical microscopy, and white light interferometry. The deposition rate was about 1 micron /hr. Computational fluid dynamics software Fluent was used to understand and simulate gas flow inside the reactor chamber and to optimize the deposition process. [Preview Abstract] |
Tuesday, March 6, 2007 4:42PM - 4:54PM |
L17.00010: Molecular Dynamics Simulations of Nanomolding Process Jan-Michael Carrillo, Andrey Dobrynin The process of nanomolding hydrophobic monomers and polymers is studied by molecular dynamics simulations. A thin film with a monomer density of 0.524 $\sigma ^{-3}$ consisting of monomers or polymer chains with different degrees of polymerization is prepared by NVT-ensemble simulations. The mold is created by pressing the substrate with attached spherical nanoparticles, representing a master, into thin film. To fix the mold structure the film is crosslinked at different crosslinking densities. The nanoparticle pattern is recovered by molding a similar thin film into the crosslinked mold. The quality of the molding process is evaluated by calculating the eigenvalues of the radius of gyration tensor of the molded nanoparticles as a function of the crosslinking density, degree of polymerization and Lennard-Jones interaction parameters. [Preview Abstract] |
Tuesday, March 6, 2007 4:54PM - 5:06PM |
L17.00011: Morphology development in electrospun nanofibers Thein Kyu, Pratyush Dayal The present article presents the modeling and simulation of the kinetics of electro- spinning process in conjunction with the spatio-temporal evolution of fiber morphology driven by phase separation. The spinning process has been modeled based on an array of beads connected by Maxwell's elements in cylindrical coordinates to describe the viscous retracting force counter-balanced by the Columbic forces representing the repulsive electrostatic charges. The dynamics of phase separation in the unstable region of a polymer solution has been calculated based on the Cahn-Hilliard time evolution equation. The simulation based on the coupling of these two processes has revealed the formation of porous voids, concentration bands perpendicular to the spinline (similar to banded textures) and along the spinline leading to splitting of the electro-spun fiber into nanofibrillar strands. [Preview Abstract] |
Tuesday, March 6, 2007 5:06PM - 5:18PM |
L17.00012: Production of bi-component core-sheath nanofibers using Chitosan and Polyethylene oxide Satyajeet Ojha, Derrick Stevens, Laura Clarke, Russell Gorga There has been a renewed interest to develop fibers at nanometer scale due to the large number of potential biomedical uses such as tissue engineering, drug delivery and wound care applications. Chitosan is a naturally occurring polysaccharide obtained from crustaceans. Its antibacterial properties have been acknowledged. Our effort has been to develop core-sheath nanofibers using chitosan, and poly (ethylene oxide) (PEO), another bio-compatible polymer. The critical properties and parameters such as feed rate, electric field, distance between needle and grounded collector and their consequences on morphology are discussed. Chitosan/PEO solutions have been characterized by surface tension, molecular weight and viscosity which are crucial factors to achieve core-sheath geometry. Tensile and conductive properties of these core-sheath nanofibers have been investigated which could be important for them to be used in wound scaffolds and cell-culture respectively. [Preview Abstract] |
Tuesday, March 6, 2007 5:18PM - 5:30PM |
L17.00013: Coarse Grained Modelling of Nanotube Stabilization by PEO Adsorption and Grafting Justin Hooper, Dmitry Bedrov, Grant Smith Coarse grained, implicit solvent models have been developed to represent the interaction between two infinite (periodic) single-walled carbon nanotubes and poly(ethylene oxide) in an aqueous environment. The polymer is modelled at a monomeric level of granularity, while the nanotubes are represented as cylindrical effective fields anchored to infinite, periodic lines. This coarse-grained model has been utilized to determine the potential of mean force between two nanotubes with either freely adsorbing or grafted polymer association models. The similarities and differences in relative stabilization of the nanotubes due to the polymer presence and association method is discussed. [Preview Abstract] |
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