Stress-enhanced mobility and dynamic yielding in polymer glasses

Abstract

A statistical mechanical theory is proposed for stress-induced acceleration of thermally driven barrier hopping and segmental relaxation, dynamic yielding and devitrification in polymer glasses. The approach is built on the concept of a nonequilibrium free energy determined by the amplitude of temperature-dependent collective density fluctuations, and the idea that stress induces an instantaneous force on a segment. Multiple predictions that fundamentally differ from the phenomenological Eyring model are made for the temperature and strain rate dependence of the dynamic yield stress and deformation modified segmental relaxation time, which are in accord with experiments and simulations.