Cooperative Dynamics in Polymer Fluids: Melts, Blends, and their Glass Transition

University Of Oregon Eugene, Eugene OR

Investigators

Abstract

This grant supports theoretical research for the development of a rigorous microscopic approach to describe polymer dynamics in structurally homogeneous, but dynamically heterogeneous polymer melts and blends as a function of their chemical structure and of the thermodynamic conditions. The achievement of a molecular level understanding of the properties of polymer melts and blends is relevant for the development of new materials. This research is an extension of the original approach developed over the past few years of the prior grant, where the equations were formalized and the dynamics of unentangled polymer melts were investigated. For the first time, we were able to describe quantitatively the onset of anomalous dynamics observed in computer simulations and experiments of unentangled polyethylene dynamics. For the new research we focus on extending our approach to describe the motion of dynamically heterogeneous fluids in polymer melts, undercooled polymer melts and polymer blends. The presence of dynamical heterogeneities, increasing in size with decreasing temperature, appears to be the mechanism responsible for the onset of the glass transition. A study of the interplay between heterogeneous dynamics and concentration fluctuations is likely to explain the dynamical anomalies present in structurally homogeneous polymer blends, such as the breaking of time-temperature superposition. %%% This grant supports a theoretical investigation of the dynamical response of polymer systems. The theory developed will fill an important gap in the desciption of these materials and should have wide application. ***