Structure and scaling laws of liquid/vapor interfaces close to the critical point

TL;DR

This paper introduces a new density-based length scale for fluid interfaces near the critical point, revealing different fluctuation regimes and improving understanding of capillary wave behavior.

Contribution

It proposes an unsupervised learning-derived length scale that diverges mildly near the critical point, distinguishing fluctuation regimes in fluid interfaces.

Findings

The new length scale follows a specific scaling law near the critical point.

It effectively separates intrinsic fluctuations from capillary waves.

The approach enhances understanding of interface fluctuations close to criticality.

Abstract

To reach a deeper understanding of fluid interfaces it is necessary to identify a meaningful coarse-graining length that separates intrinsic fluctuations from capillary ones, given the lack of a proper statistical mechanical definition of the latter. Here, with the help of unsupervised learning techniques, we introduce a new length scale based on the local density of the fluid. This length scale follows a scaling law that diverges more mildly than the bulk correlation length upon approaching the critical point. This allows to distinguish regimes of correlated and uncorrelated capillary waves from that of intrinsic fluctuations.