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Kovacs effect in glass with material memory revealed in non-equilibrium particle interactions

Lulli, Matteo, Lee, Chun-Shing, Zhang, Ling-Han, Deng, Hai-Yao ORCID: and Lam, Chi-Hang 2021. Kovacs effect in glass with material memory revealed in non-equilibrium particle interactions. Journal of Statistical Mechanics: Theory and Experiment 2021 (9) , 093303. 10.1088/1742-5468/ac1f26

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The Kovacs effect is a remarkable feature of the ageing dynamics of glass forming liquids near the glass transition temperature. It consists in a non-monotonous evolution of the volume/enthalpy after a succession of two abrupt temperature changes: first from a high initial temperature Ti to a much lower annealing temperature Ta followed by a smaller second jump back to a slightly higher final temperature Tf. The second change is performed when the instantaneous value of the volume/enthalpy coincides with the equilibrium one at the final temperature. While this protocol might be expected to yield equilibrium dynamics right after the second temperature change, one observes the so-called Kovacs hump in glassy systems. In this paper we apply such thermal protocol to the distinguishable particles lattice model for a wide range of fragility of the system. We study the Kovacs hump based on energy relaxation and all main experimental features are captured. Results are compared to general predictions based on a master equation approach in the linear response limit. We trace the origin of the Kovacs hump to the non-equilibrium nature of the probability distribution of particle interaction energies after the annealing and find that its difference with respect to the final equilibrium distribution is non-vanishing with two isolated zeros. This allows Kovacs' condition of equilibrium total energy to be met out-of-equilibrium, thus representing the memory content of the system. Furthermore, the hump is taller and occurs at a larger overlap with the system initial configuration for more fragile systems. The dynamics of a structural temperature for the mobile regions strongly depends on the glass fragility while for the immobile ones only a weak dependence is found.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Publisher: IOP Publishing
ISSN: 1742-5468
Date of First Compliant Deposit: 23 September 2021
Date of Acceptance: 6 August 2021
Last Modified: 09 Nov 2023 22:07

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