Configuration and Dynamics in Large Polymer Systems

University Of Akron, Akron OH

Investigators

Abstract

0098321 Mattice New types of catalysts permit the tailoring of the atomisticially detailed structure of known polymers in ways that were not previously possible. The properties of the resulting polymers are often strongly affected by these changes. The properties have their origin at distance scales on the order of a few tenths of a nm, because it is on this distance scale that the atomistically detailed structure is defined. However, the import physical properties of bulk materials produced from these polymers arise from the mixing and organization of long chain molecules, an issue that affects much longer distance scales. The new bridging methods are required in order to connect these two distance scales. The new hierarchy will be employed to understand how these atomistically detailed changes can affect the properties of a single polymer, as illustrated by "elastomeric polypropylene", and the blends obtained upon mixing two chemically similar polymers. The change in the dynamics of polymers at the entanglement transition will be studied in a way that uniquely takes advantage of the hierarchical nature of the family of simulations. This hierarchy permits study of the interesting, but relatively slow, dynamics of the entangled system using a coarse-grained model that can unambiguously be related to an atomistically detailed structure. Therefore it becomes possible to perform laboratory experiments with precisely the same system that is the subject of the simulation. The experiments, using pulsed gradient NMR, and simulations will employ precisely the same bidisperse polyethylene melts. The unambiguous connection with experiment will provide a very strong constraint on the development of the simulation, which will cover the transition region in which the system changes from "unentangled" to "entangled" behavior. Analysis of the simulations should produce a better understanding of the changes in the types of motion polymers in this transition region. The broad range of time and distance scales covered by important properties of dense polymers has historically produced two different, and disconnected, models for these materials. Models expressed with atomistically detailed structures are limited to short distance and time scales. Phenomena at long distance and time scales are described using coarse grained models, or, for very large scales, continuum models. The project will produce a hierarchy of models that bridges between the atomistically detailed structures and a series of increasingly more coarsely grained structures that extend well into the nanoscale regime, where one sees the transition from molecular to continuum behavior.