Freezing, melting and the onset of glassiness in binary mixtures

TL;DR

This study investigates the relationship between freezing, melting, and glassy dynamics in a binary mixture, revealing that the onset of glassiness is distinct from freezing but closely related to melting, with implications for understanding glass formation.

Contribution

It provides a detailed phase diagram analysis showing the disconnect between glassiness onset and freezing, and highlights the role of melting and isomorph theory in glass-forming liquids.

Findings

Onset of glassiness does not coincide with freezing.

The onset temperature tracks the melting line.

Characteristic temperatures follow pressure dependencies predicted by isomorph theory.

Abstract

We clarify the relationship between freezing, melting, and the onset of glassy dynamics in a prototypical glass-forming mixture model. Our starting point is a precise operational definition of the onset of glassiness, as expressed by the emergence of inflections in time-dependent correlation functions. By scanning the temperature-composition phase diagram of the mixture, we find a disconnect between the onset of glassiness and freezing. Surprisingly, however, the onset temperature closely tracks the melting line, along which the excess entropy is approximately constant. At fixed composition, all characteristic temperatures display nonetheless similar pressure dependencies, which are very well predicted by the isomorph theory. While our results rule out a general connection between thermodynamic metastability and glassiness, they call for a reassessment of the role of crystalline precursors in glass-forming liquids.