Microscopic theory of convective constraint release

We develop a microscopic description of the contribution to stress relaxati on in entangled polymer melts of convective constraint release, which is th e release of entanglement constraints due to the effects of convective flow on chains surrounding a given chain. Our theory resolves three of the main shortcomings of the Doi-Edwards model in nonlinear rheology, in that it pr edicts (1) a monotonically increasing shear stress as a function of shear r ate, (2) shear stress independent of molecular weight at sufficiently high shear rates, and (3) only modest anisotropies in the single chain scatterin g function, in agreement with experiment. In addition, our approach predict s that a stress maximum and resulting shear-banding instability would occur for living micelle solutions, as observed. (C) 2001 Thr Society of Rheolog y.