Convective constraint release (CCR) revisited

Abstract

The molecular mechanism known as convective constraint release (CCR) is here revisited to account for the fact that in fast flows topological entanglements decrease in number, as recently shown by the molecular dynamics simulations of Baig et al. [Macromolecules 43, 6886–6902 (2010)] and even before by the Brownian simulations of Yaoita et al. [J. Chem. Phys. 128, 154901 (2008)]. Based on the same Brownian dynamics code, Furuichi et al. [J. Chem. Phys. 133, 174902 (2010)] suggested that the time-strain separability in step strain relaxation is influenced by the entanglement density dynamics, an idea previously explored by Archer et al. [Macromolecules 35, 10216–10224 (2002)]. The simple model that is here proposed is therefore tested against literature data of stress relaxation following large step strains, where the time-strain separability is approached in a time much longer than the expected Rouse time, a mystery that has long remained unsolved. The new CCR theory gives a simple mathematical form to the suggestion of Furuichi et al. [J. Chem. Phys. 133, 174902 (2010)] and Archer et al. [Macromolecules 43, 6886–6902 (2002)] and also, for the first time, predicts a minimum in the time-dependent damping function, in agreement with the experiments.