Kovacs effect and the relation between glasses and supercooled liquids

TL;DR

This paper revisits the Kovacs effect in glass-forming liquids, exploring how out-of-equilibrium volume changes relate to the glass transition and its underlying mechanisms.

Contribution

It provides a theoretical analysis of the Kovacs effect, discussing its implications for understanding the nature of the glass transition and the dynamics of supercooled liquids.

Findings

Kovacs effect reflects complex out-of-equilibrium dynamics.

The phenomenon is linked to the dynamical arrest in glass-forming liquids.

Implications for the existence of an underlying phase transition.

Abstract

In this note we revisit the Kovacs effect, concerning the way in which the volume of a glass-forming liquid, which has been driven out of equilibrium, changes with time while the system evolves towards a metastable state. The theoret- ical explanation of this phenomenon has attracted much interest even in recent years, because of its relation with some subtle aspects of the still elusive nature of the glass transition. In fact, even if there is a rather general consensus on the fact that what is experimentally observed on cooling is the dramatic effect produced by the dynam- ical arrest of slower degrees of freedom over the experimental time scale, it is not yet clear whether this phenomenology can be justified upon assuming the existence of an underlying (possibly, high order) phase transition at lower temperatures.