Simultaneous memory effects in the stress and in the dielectric susceptibility of a stretched polymer glass

TL;DR

This study demonstrates complex memory effects in a stretched polymer glass, where stress and dielectric susceptibility relax non-monotonically after halting and resuming strain, revealing insights into polymer relaxation dynamics.

Contribution

It provides experimental evidence of simultaneous memory effects in stress and dielectric response, with a novel scaling approach for relaxation times in polymer glasses.

Findings

Relaxation depends on observable, strain, and waiting time.

Scaling relaxation time as t/ln(t_w) collapses data onto master curves.

Dielectric response reveals distribution of relaxation times.

Abstract

We report experimental evidence that a polymer stretched at constant strain rate $\dot\lambda$ presents complex memory effects after that $\dot\lambda$ is set to zero at a specific strain $\lambda_w$ for a duration $t_w$, ranging from $100$s to $ 2.2\times10^5$s. When the strain rate is resumed, both the stress and the dielectric constant relax to the unperturbed state non monotonically. The relaxations depend on the observable, on $\lambda_w$ and on $t_w$. Relaxation master curves are obtained by scaling the relaxation time as $t/\ln (t_w)$. The dielectric evolution also captures the distribution of the relaxation times, so the results impose strong constraints on the relaxation models of polymers under stress and they can be useful for a better understanding of memory effects in other disorder materials.