Finite-size scaling and thermodynamics of model supercooled liquids: Long-range concentration fluctuations and the role of attractive interactions

TL;DR

This study investigates how attractive interactions influence the thermodynamics and structure of supercooled liquids, revealing that attractions promote long-range fluctuations and significantly affect thermodynamic properties, especially at lower densities.

Contribution

It demonstrates that attractive forces play a crucial nonperturbative role in the thermodynamics and structure of supercooled liquids, especially in the emergence of long-range concentration fluctuations.

Findings

Attractive interactions promote long-range concentration fluctuations.

Purely repulsive systems remain miscible and lack long-range anomalies.

Thermodynamics is significantly influenced by attractive forces, not just short-range repulsions.

Abstract

We compute partial structure factors, Kirkwood-Buff integrals (KBIs) and chemical potentials of model supercooled liquids with and without attractive interactions. We aim at investigating whether relatively small differences in the tail of the radial distribution functions result in contrasting thermodynamic properties. Our results suggest that the attractive potential favours the nucleation of long-range structures. Indeed, upon decreasing temperature, Bathia-Thornton structure factors display anomalous behaviour in the $k\to 0$ limit. KBIs extrapolated to the thermodynamic limit confirm this picture, and excess coordination numbers identify the anomaly with long-range concentration fluctuations. By contrast, the purely repulsive system remains perfectly miscible for the same temperature interval and only reveals qualitatively similar concentration fluctuations in the crystalline state. Furthermore, differences in both isothermal compressibilities and chemical potentials show that thermodynamics is not entirely governed by the short-range repulsive part of the interaction potential, emphasising the nonperturbative role of attractive interactions. Finally, at higher density, where both systems display nearly identical dynamical properties and repulsive interactions become dominant, the anomaly disappears, and both systems also exhibit similar thermodynamic properties.