Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session A20: Invited Session: Interfacing Experiment and Theory in Polymer Physics |
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Sponsoring Units: DPOLY Chair: Bryan Boudouris, Purdue University Room: Ballroom B |
Monday, March 2, 2015 8:00AM - 8:36AM |
A20.00001: Order and Disorder in Short Block Polymers Invited Speaker: Frank S. Bates Block polymers have captivated the interest of scientists and engineers for more than half a century. The phase behavior of this class of self-assembling soft material is well understood in the limit of infinite molecular weight, based on the self-consistent mean-field theory pioneered by Leibler. At practical molecular sizes, typically around N $\approx $ 1000 repeat units, fluctuation effects become highly significant in the vicinity of the order disorder transition. One-loop corrections to mean-field theory, first described by Brazovski and applied to block polymers by Fredrickson and Helfand, are not expected to be applicable in this limit. Moreover, the drive towards ever smaller domain dimensions, and the opportunity to circumvent transport limitations associated with entanglements, have motivated experiments with yet lower molecular weight block polymers, N less than 100. This presentation will describe the consequences of fluctuations and the equilibrium structural properties of short model AB diblock polymers in the symmetric (f $=$ 1/2) and asymmetric (f $\to $ 0) regimes above and below the order-disorder transition. The consequences of fluctuations and access to equilibrium states will be described in the 1-dimensional stripped (lamellar) phase and the ordering of point particles in 3-dimensions, respectively. As N $\to $ 1 computer simulation with realistic molecular detail becomes feasible presenting exciting opportunities to compliment the associated theoretical challenges. [Preview Abstract] |
Monday, March 2, 2015 8:36AM - 9:12AM |
A20.00002: Nanocomposites with Crystalline Polymers Invited Speaker: Sanat Kumar The creation of ordered (layered) biomimetic materials typically follows a series of steps: first mix nanoparticles with water, organize the NPs by ice templating, evaporate the ice and then back fill with metal or polymer. We propose a simple method exploiting the in situ self-assembly of a crystalline polymer in the presence of nanoparticles to facilitate this process, and provide a completely new pathway for the synthesis of biomimetic materials. A suite of complementary experimental tools are used in this analysis. In parallel, we are developing theoretical tools to a priori predict the morphologies adopted by semicrystalline polymers. The convergence of these novel experimental and theoretical developments in the venerable field of semicrystalline polymers could lead to new applications for this largest class of commercially relevant polymeric materials. With Jacques Jestin, Brian Benicewicz, Dan Zhao, Longxi Zhao [Preview Abstract] |
Monday, March 2, 2015 9:12AM - 9:48AM |
A20.00003: Segmental Interactions between Polymers and Small Molecules in Batteries and Biofuel Purification Invited Speaker: Nitash Balsara Polymers such as poly(ethylene oxide) (PEO) and poly(dimethyl siloxane) (PDMS) have the potential to play an important role in the emerging clean energy landscape. Mixtures of PEO and lithium salts are the most widely studied non-flammable electrolyte for rechargeable lithium batteries. PDMS membranes are ideally suited for purifying bioethanol and biobutanol from fermentation broths. The ability of PEO and PDMS to function in these applications depends on segmental interactions between the polymeric host and small molecule guests. One experimental approach for studying these interactions is X-ray absorption spectroscopy (XAS). Models for interpreting XAS spectra of amorphous mixtures and charged species such as salts must quantify the effect of segmental interactions on the electronic structure of the atoms of interest (e.g. sulfur). This combination of experiment and theory is used to determine the species formed in during charging and discharging lithium-sulfur batteries; the theoretical specific energy of lithium-sulfur batteries is a factor of four larger than that of current lithium-ion batteries. Selective transport of alcohols in PDMS-containing membranes is controlled by the size, shape, and connectivity of sub-nanometer cavities or free volume that form and disappear spontaneously as the chain segments undergo Brownian motion. We demonstrate that self-assembly of PDMS-containing block copolymers can be used to control segmental relaxation, which, in turn, affects free volume. Positron annihilation was used to determine the size distribution of free volume cavities in the PDMS-containing block copolymers. The effect of this artificial free volume on selective permeation of alcohols formed by fermentation of sugars derived from lignocellulosic biomass is studied. Molecular dynamics simulations are needed to understand the relationship between self-assembly, free volume, and transport in block copolymers. [Preview Abstract] |
Monday, March 2, 2015 9:48AM - 10:24AM |
A20.00004: Using multi-scale molecular simulations to guide experimental design of biomaterials for drug and DNA delivery Invited Speaker: Arthi Jayaraman In this talk I will present molecular simulations studies that guide experimental synthesis of polymers for efficient DNA delivery. Viruses, while effective at delivery and transfection of DNA, can elicit harmful immunogenic responses, thus motivating design of non-viral transfection agents. Polycations are a promising class of non-viral vectors that bind to the negatively charged DNA backbone to form a complex (polyplex) that is then internalized into the target cell. Combinatorial approaches have generated various polycations with differing DNA transfection efficacies, but there is a need for general design guidelines that can relate the molecular features of the polycation to its DNA transfection efficiency. Using atomistic and coarse-grained molecular dynamics simulations we connect the thermodynamics of polycation-DNA binding and polyplex structure to experimentally observed transfection efficiency as a function of polycation chemistry and architecture. [Preview Abstract] |
Monday, March 2, 2015 10:24AM - 11:00AM |
A20.00005: Ion Containing Polymers for Battery Technology Invited Speaker: Janna K. Maranas Polymer electrolytes have potential for use in next generation lithium and sodium batteries. Replacing the liquid electrolyte currently used has several advantages: it allows use of high energy density solid lithium as the anode, removes toxic solvents, improves safety, and eliminates the need for heavy casings. Despite their advantages, the conductivity of solid polymer electrolytes is not sufficient for use in batteries. As a result, considerable effort towards improving conductivity and understanding mechanisms of lithium transport has taken place over the last 30 years. This talk considers the interplay of conductivity, crystallinity, local coordination and polymer dynamics in solid polymer electrolytes. Using a combination of experimental and computational technique, we propose the possibility of high charge mobility using ion aggregates and percolated nanofiller networks. [Preview Abstract] |
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