Simultaneous memory effects in the stress and in the dielectric susceptibility of a stretched polymer glass
We report experimental evidence that a polymer stretched at constant strain rate $\dotλ$ presents complex memory effects after that $\dotλ$ is set to zero at a specific strain $λ_w$ 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 $λ_w$ 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.