Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session F56: Invited Session: Polymer Physics Prize Symposium |
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Sponsoring Units: DPOLY Chair: Tom Witten, University of Chicago Room: Four Seasons Ballroom 4 |
Tuesday, March 4, 2014 8:00AM - 8:36AM |
F56.00001: Polymer Prize: The Many Varied Phenomena of Equilibrium Self-assembly/polymerization Invited Speaker: Karl Freed The self-assembly of molecules to form large clusters under equilibrium conditions is a ubiquitous phenomenon that impacts numerous systems of interest in physics, chemistry, and biology. While not a true phase transition, equilibrium self-assembly bears similarities to phase transitions but requires quite separate treatment. The simplest theory of self-assembly is provided by Flory-Huggins theory in which structureless monomers assemble into clusters of i-monomers, i$=$2,\textellipsis ,$\infty $. Despite its simplicity, the theory explains many experimental findings for a rich variety of different self-assembling systems, including the polymerization of actin, the influence of thermal activation, chemical initiation, hierarchical self-assembly, ring formation, soft interactions, crowding, and adsorption onto surfaces on the thermodynamics of self-assembling systems, the interplay between self-assembly and phase separation, the nature of cooperativity, and more. Extensions of the simplest theory are being developed for strongly interacting systems and for describing the evolution of non-equilibrium systems. [Preview Abstract] |
Tuesday, March 4, 2014 8:36AM - 9:12AM |
F56.00002: Polymer dynamics in turbulent flow Invited Speaker: Murugappan Muthukumar Presence of dilute amounts of high-molecular weight polymers in liquids undergoing turbulent wall-bounded shear flows leads to significant drag reduction. There are two major proposed mechanisms of drag reduction in the literature. One is based on enhanced viscosity due to chain extension; the other is based on the assumption that elastic energy stored in polymer conformations is comparable to the kinetic energy in some eddies. Using the Navier-Stokes equation for the fluid and the Kirkwood-Riseman-Zimm equation for polymer chains, we have addressed the coupling between the near-wall turbulence dynamics and polymer dynamics. Our theoretical results show that the torque associated with polymer conformations contributes more significantly than the chain stretching and that the characteristic dimensions of polymer coils are much smaller than eddy sizes required for possible exchange of energy. We thus emphasize an additional mechanism to the existing two schools of thought in the search of an understanding of drag reduction. [Preview Abstract] |
Tuesday, March 4, 2014 9:12AM - 9:48AM |
F56.00003: Path-Integration Computation of the Transport Properties of Polymers Nanoparticles and Complex Biological Structures Invited Speaker: Jack Douglas One of the things that puzzled me when I was a PhD student working under Karl Freed was the curious unity between the theoretical descriptions of excluded volume interactions in polymers, the hydrodynamic properties of polymers in solution, and the critical properties of fluid mixtures, gases and diverse other materials (magnets, superfluids,etc.) when these problems were formally expressed in terms of Wiener path integration and the interactions treated through a combination of epsilon expansion and renormalization group (RG) theory. It seemed that only the interaction labels changed from one problem to the other. What do these problems have in common? Essential clues to these interrelations became apparent when Karl Freed, myself and Shi-Qing Wang together began to study polymers interacting with hyper-surfaces of continuously variable dimension where the Feynman perturbation expansions could be performed through infinite order so that we could really understand what the RG theory was doing. It is evidently simply a particular method for resuming perturbation theory, and former ambiguities no longer existed. An integral equation extension of this type of exact calculation to ``surfaces'' of arbitrary fixed shape finally revealed the central mathematical object that links these diverse physical models- the capacity of polymer chains, whose value vanishes at the critical dimension of 4 and whose magnitude is linked to the friction coefficient of polymer chains, the virial coefficient of polymers and the 4-point function of the phi-4 field theory,\textellipsis Once this central object was recognized, it then became possible solve diverse problems in material science through the calculation of capacity, and related ``virials'' properties, through Monte Carlo sampling of random walk paths. The essential ideas of this computational method are discussed and some applications given to non-trivial problems: nanotubes treated as either rigid rods or ensembles worm-like chains having finite cross-section, DNA, nanoparticles with grafted chain layers and knotted polymers. The path-integration method, which grew up from research in Karl Freed's group, is evidently a powerful tool for computing basic transport properties of complex-shaped objects and should find increasing application in polymer science, nanotechnological applications and biology. [Preview Abstract] |
Tuesday, March 4, 2014 9:48AM - 10:24AM |
F56.00004: Temperature Dependence of Structural Relaxation: From ``Super-fragile'' Polymers to ``Super-strong'' Behavior of Water Invited Speaker: Alexei Sokolov The microscopic mechanism of the steep temperature dependence of structural relaxation upon approaching Tg still remains a puzzle in the field of dynamics of polymers and soft materials in general. The steepness of the temperature behavior and its deviation from classical Arrhenius law is usually characterized by the fragility index m. This contribution presents an overview of several models proposed to connect molecular parameters to the fragility. We emphasize the Generalized Entropy Theory [1] and its prediction on the role of chain packing in fragility of polymers. Based on this theory and many experimental studies we unravel the role of chain structure, intermolecular interactions and molecular weight in polymer fragility [2,3], providing a qualitative explanations of why many polymers exhibit extremely fragile behavior. Next we show that similar qualitative ideas about frustration in packing might be applicable to other glass forming systems. In the last part we discuss the recent discovery of ``super-strong'' behavior of deeply supercooled water and the role of quantum effects in this anomalously low fragility.\\[4pt] [1] Stukalin, E. B.; Douglas, J. F.; Freed, K. F. \textbf{J. Chem. Phys. 131}, 114905 (2009).\\[0pt] [2] K. Kunal, et al., \textbf{Macromolecules 41}, 7232 (2008).\\[0pt] [3] A. Agapov, et al., \textbf{Macromolecules 45}, 8430 (2012). [Preview Abstract] |
Tuesday, March 4, 2014 10:24AM - 11:00AM |
F56.00005: Interactive Phase Separation and Crystallization: from Dynamically Symmetric to Dynamically Asymmetric Blend Systems Invited Speaker: Charles C. Han Crystallization and phase separation are two intriguing phase transitions in nature and have been intensively studied in the past decades. Recently, the mechanism of simultaneous or interactive transitions of crystallization and phase separation of binary blend has became a popular research topic due to its importance to both fundamental understandings as well as technological applications. In this presentation, interactive phase separation and crystallization will be discussed. Situations where the two components are dynamically similar (symmetric) and dis-similar (un-symmetric) will be compared. Some interesting pattern formation, step-wise growth mechanism, and structure/morphology formation mediated under the competition between thermodynamic perturbation and asymmetric viscoelasticity will be presented. [Preview Abstract] |
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