Revealing Liquid-Gas Transitions with Finite-Size Scaling in Confined Systems

TL;DR

This paper introduces a finite-size scaling method based on density profiles to reliably identify liquid-gas phase transitions in confined systems, overcoming ambiguities caused by external fields.

Contribution

The authors propose a novel finite-size scaling criterion using density profile collapse and intersection to distinguish between single-phase and two-phase systems.

Findings

Scaling collapses density profiles for one-phase systems.

Profiles intersect at interfaces in two-phase systems.

Validated with experiments and simulations of colloids and plasmas.

Abstract

The application of an external field often renders empirical criteria for identifying liquid-gas phase transitions ambiguous. Here, we demonstrate that the finite-size scaling of the density profile provides a definitive criterion to distinguish liquid-gas coexistence from a single fluid phase in field-confined systems. Our scaling method collapses the density profiles of different system sizes onto a single master curve for a one-phase system, while causing the profiles to intersect at the interface in a two-phase system. We validate this theoretical proposal through experiments and simulations of two model systems: colloidal suspensions under gravity and/or two-dimensional complex plasmas confined by a central potential. Our method is broadly applicable for detecting liquid-gas phase transitions in laboratory systems where external fields are inherent.