A microscopic view of deformation-accelerated dynamics in polymer glasses

When amorphous polymers are deformed, the slow glassy dynamics resulting from broad distributions of relaxation times becomes accelerated and permits plastic flow. We use molecular dynamics simulations as a computational microscope to obtain insight into the origin of the deformation-accelerated dynamics and its relationship to aging in a model polymer glass. Segmental trajectories are analyzed to identify individual relaxation events, and the full distribution of relaxation times is obtained under three deformation protocols: step stress (creep), step strain, and constant strain rate deformation. As in experiments, the dynamics are accelerated by several orders of magnitude by the deformation, and a narrowing of the distribution of relaxation times during creep is directly observed. Additionally, the acceleration factor describing the transformation of the relaxation time distributions was computed and found to obey a universal dependence on the strain, independent of the age and deformation protocol.