Critical surface adsorption of confined binary liquids with locally conserved mass and composition

TL;DR

This study uses molecular dynamics simulations to analyze surface adsorption profiles of confined binary liquids near a critical point, revealing critical scaling behavior and monotonic order parameter decay consistent with theoretical predictions.

Contribution

It provides the first detailed molecular dynamics analysis of critical surface adsorption in confined binary liquids with local mass and composition conservation.

Findings

Order parameter profiles decay monotonically near surfaces.

Results qualitatively agree with mesoscopic field-theoretical predictions.

Critical scaling behavior observed near the bulk consolute point.

Abstract

Close to a solid surface, the properties of a fluid deviate significantly from their bulk values. In this context, we study the surface adsorption profiles of a symmetric binary liquid confined to a slit pore by means of molecular dynamics simulations; the latter naturally entails that mass and concentration are locally conserved. Near a bulk consolute point, where the liquid exhibits a demixing transition with the local concentration as the order parameter, we determine the order parameter profiles and characterise the relevant critical scaling behaviour, in the regime of strong surface attraction, for a range of pore widths and temperatures. The obtained order parameter profiles decay monotonically near the surfaces, also in the presence of a pronounced layering in the number density. Overall, our results agree qualitatively with recent theoretical predictions from a mesoscopic field-theoretical approach for the canonical ensemble.