Deformation-induced accelerated dynamics in polymer glasses

TL;DR

This study uses molecular dynamics simulations to explore how deformation accelerates segmental dynamics in aging polymer glasses, revealing universal acceleration behavior linked to strain and explaining aging and rejuvenation phenomena.

Contribution

It introduces a detailed analysis of relaxation time distributions under various deformation protocols, uncovering a universal acceleration factor dependent solely on strain.

Findings

Deformation accelerates dynamics by several orders of magnitude.

Mechanical rejuvenation erases aging effects during yield.

Relaxation time distributions can be universally scaled by strain.

Abstract

Molecular dynamics simulations are used to investigate the effects of deformation on the segmental dynamics in an aging polymer glass. Individual particle trajectories are decomposed into a series of discontinuous hops, from which we obtain the full distribution of relaxation times and displacements under three deformation protocols: step stress (creep), step strain, and constant strain rate deformation. As in experiments, the dynamics can be accelerated by several orders of magnitude during deformation, and the history dependence is entirely erased during yield (mechanical rejuvenation). Aging can be explained as a result of the long tails in the relaxation time distribution of the glass, and similarly, mechanical rejuvenation is understood through the observed narrowing of this distribution during yield. Although the relaxation time distributions under deformation are highly protocol specific, in each case they may be described by a universal acceleration factor that depends only on the strain.