9629901 Colby This grant will explore the area of dynamics and rheology in polymer blends. Recent experiments have shown that miscible blends have complex rheology. One manifestation of this is the breakdown of the empirical time-temperature superposition principle, known to be valid for homopolymer systems. Recent theory suggests that the themorheological complexity in blends is driven at the segmental level by concentration fluctuations, coupled to differences in the glass transition temperatures of the components. The goal of the experimental portion of the proposed research is to carefully measure concentration fluctuations (using small angle neutron scattering), local segmental dynamics (using dielectric spectroscopy) and terminal dynamics (using forward recoil spectroscopy diffusion measurements and linear viscoelasticity) to systematically test the proposed relation between concentration fluctuations and dynamics in miscible blends. The theoretical component of the proposed work will extend previous concentration fluctuation ideas, which currently only model dynamics at the segmental level, to predict terminal dynamics (relaxation of entire chains). Computer simulations will also be used to elucidate the role of different variables in the dynamics of miscible blends. %%% Since polymer blends are seeing increased use in practical applications, it is important that a quantitative understanding of their rheology be obtained so as to assist in their processing. The long-term goal is to develop a complete molecular model forlthe rheology of miscible polymer blends. ***
