Kovacs effects in an aging molecular liquid

TL;DR

This study uses molecular dynamics simulations to investigate the Kovacs effect in an aging molecular liquid, revealing non-monotonic volume evolution and landscape exploration differences from equilibrium, with implications for glass thermodynamics.

Contribution

It provides the first simulation-based evidence of Kovacs effects in a molecular liquid and links these phenomena to potential energy landscape properties.

Findings

Non-monotonic volume evolution observed during aging.

System explores different potential energy regions out of equilibrium.

Implications for understanding glass thermodynamics.

Abstract

We study by means of molecular dynamics simulations the aging behavior of a molecular model of ortho-terphenyl. We find evidence of a a non-monotonic evolution of the volume during an isothermal-isobaric equilibration process, a phenomenon known in polymeric systems as Kovacs effect. We characterize this phenomenology in terms of landscape properties, providing evidence that, far from equilibrium, the system explores region of the potential energy landscape distinct from the one explored in thermal equilibrium. We discuss the relevance of our findings for the present understanding of the thermodynamics of the glass state.