NMR Investigation of Segmental Dynamics in Multicomponent Systems

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

In multicomponent systems, the molecular motion of a polymer may be strongly affected by the presence of other synthetic polymers, solid substrates, fillers, or biological structures. Such changes in dynamics significantly influence transport and mechanical properties. The long term goal of this research is to understand how to predict the changes in polymer dynamics which occur with mixing. Multicomponent polymer systems exhibit complex dynamics. Significant progress can be made by fully characterizing the dynamics of a number of model mixtures. The proposed research will characterize: 1) segmental dynamics of both components in a model one-phase blend (low molecular weight polystyrene/polyisoprene); 2) longer length and time scale motions of both components in a model one-phase blend; 3) segmental dynamics in the limit of infinite dilution for several one-phase blends with polyisoprene as the minor component; 4) structure and dynamics of a model nano-composite (C60/polybutadiene). In addition, two key conceptual aspects of blend dynamics will addressed: 1) the correlation between local mobility and local structure in a miscible blend (polyisoprene/polyvinylethylene); 2) the size of the regions which determine local mobility. Characterizing dynamics in complex mixtures requires the coordinated application of a number of different experimental techniques. The proposed research primarily relies upon multiple field NMR relaxation time measurements and solid-state NMR measurements of segmental and normal model motion, and neutron scattering to assess aggregation in a nanoscale composite. %%% This line of research should lead to an understanding of the complex features and useful properties of miscible polymer blends, and ultimately the ability to predict these properties. Insights from the study of a model nano-composite could lead to the ability to predict transport properties of ions and small molecules near nano-devices in contact with polymers. Comparisons between dynamics experiments and molecular dynamics computer simulations will lead to improved forcefields and the ability to perform more accurate simulation in materials science and beyond