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arXiv · 1909.03685

Spatial heterogeneities in structural temperature cause Kovacs expansion gap paradox in aging of glasses

Matteo Lulli·Chun-Shing Lee·Hai-Yao Deng·Cho-Tung Yip·Chi-Hang Lam
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Abstract

Volume and enthalpy relaxation of glasses after a sudden temperature change has been extensively studied since Kovacs seminal work. One observes an asymmetric approach to equilibrium upon cooling versus heating and, more counter-intuitively, the expansion gap paradox, i.e. a dependence on the initial temperature of the effective relaxation time even close to equilibrium when heating. Here we show that a distinguishable-particles lattice model can capture both the asymmetry and the expansion gap. We quantitatively characterize the energetic states of the particles configurations using a physical realization of the fictive temperature called the structural temperature, which, in the heating case, displays a strong spatial heterogeneity. The system relaxes by nucleation and expansion of warmer mobile domains having attained the final temperature, against cooler immobile domains maintained at the initial temperature. A small population of these cooler regions persists close to equilibrium, thus explaining the paradox.

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Matteo Lulli, Chun-Shing Lee, Hai-Yao Deng, Cho-Tung Yip, Chi-Hang Lam. 2019-09-09. Spatial heterogeneities in structural temperature cause Kovacs expansion gap paradox in aging of glasses. https://doi.org/10.1103/physrevlett.124.095501

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