Theoretical Approaches to Bridge Timescales in Polymer Dynamics

University Of Oregon Eugene, Eugene OR

Investigators

Abstract

TECHNICAL SUMMARY: This award supports theoretical research and education in statistical and dynamical properties of polymers. The work is supported by the Division of Chemistry and the Division of Materials Research. The theory enhances the basic ability to predict macroscopic properties, as measured experimentally or described in computer simulations, based on the microscopic molecular structure and physical parameters. The research uses traditional methods of equilibrium (integral equations) and non-equilibrium statistical mechanics. Guenza and coworkers employ an original approach to describe the cooperative dynamics of a group of interacting macromolecules in dynamically heterogeneous environments, i.e. the Cooperative Dynamics Generalized Langevin Equation (CDGLE). This is a microscopic, site-specific, mean-field theory, which has successfully explained the experimentally observed center-of-mass anomalous diffusion in polymer melts, and the anomalous relaxation of their normal modes, on the basis of intermolecular time-dependent correlation, originated from the dynamically heterogeneous nature of polymer liquids. The research develops along three main lines or subprojects. The first focuses on testing CDGLE and extending its range of applicability to liquid of polymers with increasing degree of polymerization, i.e. across the unentangled-to-entangled transition. In the second line, CDGLE is modified to describe polymer dynamics in dilute solutions, including polymers of biological significance such as proteins. Intramolecular potentials are derived from molecular dynamics computer simulations. This research will build on past success where the theory has been able to make predictions in good quantitative agreement with experimental data of NMR relaxation, X-ray Debye?Waller temperature factors and NMR order-parameters for the test protein CheY. Further testing against different proteins and other experimental data is undertaken to ensure the generality of the approach. Finally, the third subproject extends the coarse-graining procedure, developed by Guenza and coworkers, which maps polymers into collections of interacting soft-colloidal particles. This procedure provides the effective intermolecular potential entering CDGLE. The approach is extended to include a refined intramolecular coarse-graining and the development of a procedure for multiscale modeling of polymer liquids. The impact of the project extends beyond the research. The development of this project produces computer codes which predict these polymer properties. Once tested, the codes will be available to the scientific community through a user-friendly website. The project is an opportunity for the PI to continue her efforts to engage women and minorities as she has done in past research projects. Because the work is design to have realistic consequences, there are close collaborations with experimental groups which further enhances the value of the professional experience for the students in the project. Students are also involved in outreach activities to publicize their research. NONTECHNICAL SUMMARY: This award supports theoretical research and education in statistical and dynamical properties of polymers. The work is supported by the Division of Chemistry and the Division of Materials Research. The theory enhances the basic ability to predict material properties, as measured experimentally or described in computer simulations, based on the molecular structure and physical parameters of constituent polymer molecules. The use of a unified approach to polymer dynamics aids in developing a comprehensive understanding of polymer motion. The latter has been a long-standing goal of both practical and fundamental interest in polymer physics, since all polymeric materials (fibers, plastics, coating materials, etc.) are processed in their liquid state. The goal is to provide a theoretical tool that formally connects the effect of chemical parameters (e.g., polymer type, weight, concentration, and temperature) to the global properties (e.g., ease of flow, hardening temperature). The tools developed will be useful in designing custom-tailored polymeric materials of synthetic or biological significance. The impact of the project extends beyond the research. The development of this project produces computer codes which predict these polymer properties. Once tested, the codes will be made available to the scientific community through a user-friendly website. The project is an opportunity for the PI to continue her efforts to engage women and minorities as she has done in past research projects. Because the work is design to have realistic consequences, there are close collaborations with experimental groups which further enhances the value of the professional experience for the students in the project. Students are also involved in outreach activities to publicize their research.