Evidence of growing spatial correlations during the aging of glassy glycerol

TL;DR

This study investigates how the nonlinear dielectric susceptibility of glycerol evolves with aging, revealing an increase in correlated molecular regions and providing insights into the relationship between length and time scales in glasses.

Contribution

It demonstrates that the amplitude of nonlinear susceptibility grows with age, indicating increasing spatial correlations during glass aging, a novel insight into glassy dynamics.

Findings

N_corr increases by ~10% from 1 ks to 100 ks aging.

Linear susceptibility scaling with relaxation time breaks down for χ_3.

Evidence of growing spatial correlations during aging in glycerol.

Abstract

We have measured, as a function of the age $t_a$, the aging of the nonlinear dielectric susceptibility $\chi_3$ of glycerol below the glass transition. Whereas the linear susceptibility can be accurately accounted for in terms of an age dependent relaxation time $\tau_{\alpha}(t_a)$, this scaling breaks down for $\chi_3$, suggesting an increase of the amplitude of $\chi_3$. This is a strong indication that the number $N_{corr}$ of molecules involved in relaxation events increases with $t_a$. For $T=0.96 \times T_g$, we find that $N_{corr}$ increases by $\sim 10%$ when $t_a$ varies from $1\mathrm{ks}$ to $100\mathrm{ks}$. This sheds new light on the relation between length scales and time scales in glasses.