Memory in the aging of a polymer glass

TL;DR

This study investigates the memory effects in the dielectric properties of aging polymer glass (PMMA), revealing hysteresis, relaxation, and history-dependent behavior during temperature cycling, with implications for understanding glassy dynamics.

Contribution

It demonstrates memory effects in dielectric measurements of polymer glass, highlighting similarities and differences with spin glass behavior, and advances understanding of aging in amorphous materials.

Findings

Cooling and heating show hysteresis in dielectric constant.

Temporary cooling stops cause downward relaxation of dielectric constant.

Memory of aging persists during reheating, independent of cooling history.

Abstract

Low frequency dielectric measurements on plexiglass (PMMA) show that cooling and heating the sample at constant rate give an hysteretic dependence on temperature of the dielectric constant $\epsilon$. A temporary stop of cooling produces a downward relaxation of $\epsilon$. Two main features are observed i) when cooling is resumed $\epsilon$ goes back to the values obtained without the cooling stop (i.e. the low temperature state is independent of the cooling history) ii) upon reheating $\epsilon$ keeps the memory of the aging history ({\it Memory}). The analogies and differences with similar experiments done in spin glasses are discussed.