Strongly correlating liquids and their isomorphs

TL;DR

This paper reviews the properties of strongly correlating liquids, emphasizing their experimental predictions and the concept of isomorphs, which relate to their dynamic and thermodynamic behaviors, especially in glass-forming liquids.

Contribution

It provides a comprehensive summary of the properties and experimental predictions for strongly correlating liquids, highlighting the role of isomorphs and the isomorph filter in understanding their behavior.

Findings

Strong correlations between virial and potential energy fluctuations.

Predictions include density scaling and isochronal superposition.

Strongly correlating liquids are approximately single-parameter liquids.

Abstract

This paper summarizes the properties of strongly correlating liquids, i.e., liquids with strong correlations between virial and potential energy equilibrium fluctuations at constant volume. We proceed to focus on the experimental predictions for strongly correlating glass-forming liquids. These predictions include i) density scaling, ii) isochronal superposition, iii) that there is a single function from which all frequency-dependent viscoelastic response functions may be calculated, iv) that strongly correlating liquids are approximately single-parameter liquids with close to unity Prigogine-Defay ratio, and v) that the fictive temperature initially decreases for an isobaric temperature up jump. The "isomorph filter", which allows one to test for universality of theories for the non-Arrhenius temperature dependence of the relaxation time, is also briefly discussed.