Evidence of growing spatial correlations during the aging of glassy glycerol

Abstract

We have measured, as a function of the age $t_a$, the aging of the nonlinear dielectric susceptibility $\ddot{I}{‡}_3$ of glycerol below the glass transition. Whereas the linear susceptibility can be accurately accounted for in terms of an age dependent relaxation time $\ddot{I}{„}_{\hat{I}}\pm (t_a)$, this scaling breaks down for $\ddot{I}{‡}_3$, suggesting an increase of the amplitude of $\ddot{I}{‡}_3$. 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.

Accepted in Physical Review Letters