Density functional study of complete, first-order and critical wedge filling transitions

TL;DR

This study uses density functional theory to analyze different types of wedge filling transitions, revealing how wall-fluid interactions influence whether the filling is first-order or second-order, with results matching theoretical predictions.

Contribution

It provides a detailed numerical investigation of wedge filling transitions considering various wall-fluid interactions, extending understanding of wetting and filling phenomena near critical points.

Findings

Hard wall wedge is fully filled by vapor near coexistence.

Strong attractive interactions lead to first-order filling transitions.

Weak interactions result in second-order filling with critical exponents matching theory.

Abstract

We present numerical studies of complete, first-order and critical wedge filling transitions, at a right angle corner, using a microscopic fundamental measure density functional theory. We consider systems with short-ranged, cut-off Lennard-Jones, fluid-fluid forces and two types of wall-fluid potential: a purely repulsive hard wall and also a long-ranged potential with three different strengths. For each of these systems we first determine the wetting properties occurring at a planar wall including any wetting transition and the dependence of the contact angle on temperature. The hard wall corner is completely filled by vapour on approaching bulk coexistence and the numerical results for the growth of the meniscus thickness are in excellent agreement with effective Hamiltonian predictions for the critical exponents and amplitudes, at leading and next-to-leading order. In the presence of the attractive wall-fluid interaction, the corresponding planar wall-fluid interface exhibits a first-order wetting transition for each of the interaction strengths considered. In the right angle wedge geometry the two strongest interactions produce first-order filling transitions while for the weakest interaction strength, for which wetting and filling occur closest to the bulk critical point, the filling transition is second-order. For this continuous transition the critical exponent describing the divergence of the meniscus thickness is found to be in good agreement with effective Hamiltonian predictions.