Two-Order-Parameter Description of Liquids: Critical Phenomena and Phase Separation of Supercooled Liquids

TL;DR

This paper proposes a two-parameter model using density and bond order to better describe liquids, explaining phenomena like density fluctuations and phase separation in supercooled liquids.

Contribution

It introduces a novel two-order-parameter framework for liquids, challenging the traditional single-parameter approach based solely on density.

Findings

Explains large-scale density fluctuations in supercooled liquids.

Provides a physical basis for phase separation into two liquid phases.

Highlights the importance of bond order in liquid behavior.

Abstract

Because of the isotropic and disordered nature of liquids, the anisotropy hidden in intermolecular interactions are often neglected. Accordingly, the order parameter describing a simple liquid has so far been believed to be only density. In contrast to this common sense, we propose that two order parameters, namely, density and bond order parameters, are required to describe the phase behavior of liquids since they intrinsically tend to form local bonds. This model gives us clear physical explanations for two poorly-understood phenomena in supercooled liquids: (i) large-scale density fluctuations and (ii) phase separation of a one-component liquid into two liquid phases.