Shear-induced overaging in a polymer glass

TL;DR

This study demonstrates shear-induced overaging in a polymer glass, showing that transient shear strains can significantly slow relaxation modes, with effects depending on deformation size and linked to jammed state physics.

Contribution

The paper provides simulation evidence of shear-induced overaging in polymer glasses, highlighting the transition from elastic to plastic deformation and its impact on relaxation dynamics.

Findings

Relaxation times increase exponentially with shear deformation.

Overaging correlates with increased pressure, bond order, and inherent structure energy.

Behavior transition from elastic to plastic deformation relates to jammed state physics.

Abstract

A phenomenon recently coined as ``overaging'' implies a slowdown in the collective (slow) relaxation modes of a glass when a transient shear strain is imposed. We are able to reproduce this behavior in simulations of a supercooled polymer melt by imposing instantaneous shear deformations. The increases in relaxation times $\Delta \tau_{1/2}$ rise rapidly with deformation, becoming exponential in the plastic regime. This ``overaging'' is distinct from standard aging. We find increases in pressure, bond-orientational order and in the average energy of the inherent structures ($<e_{IS}>$) of the system, all dependent on the size of the deformation. The observed change in behavior from elastic to plastic deformation suggests a link to the physics of the ``jammed state''