Condensation and evaporation transitions in deep capillary grooves

TL;DR

This study uses density functional theory to analyze how capillary condensation and evaporation transitions occur in deep grooves, revealing temperature-dependent transition orders and a covariance with wetting phenomena.

Contribution

It provides a detailed theoretical analysis of phase transitions in capillary grooves, highlighting the temperature-dependent nature and the covariance with wetting transitions.

Findings

Below $T_w$, condensation is first-order and evaporation is continuous.

Above $T_w$, both transitions are continuous with specific critical behaviors.

A covariance exists between evaporation transition above $T_w$ and complete wetting at a planar wall.

Abstract

We study the order of capillary condensation and evaporation transitions of a simple fluid adsorbed in a deep capillary groove using a fundamental measure density functional theory (DFT). The walls of the capillary interact with the fluid particles via long-ranged, dispersion, forces while the fluid-fluid interaction is modelled as a truncated Lennard-Jones-like potential. We find that below the wetting temperature $T_w$ condensation is first-order and evaporation is continuous with the metastability of the condensation being well described by the complementary Kelvin equation. In contrast above $T_w$ both phase transitions are continuous and their critical singularities are determined. In addition we show that for the evaporation transition above $T_w$ there is an elegant mapping, or covariance, with the complete wetting transition occurring at a planar wall. Our numerical DFT studies are complemented by analytical slab model calculations which explain how the asymmetry between condensation and evaporation arises out of the combination of long-ranged forces and substrate geometry.