Revealing liquid–gas transitions with finite-size scaling in experimental and simulation systems confined by an external field

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 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.