Water in nanopores. II. Liquid-vapour phase transition near hydrophobic surfaces

TL;DR

This study investigates the liquid-vapor phase transition of water near hydrophobic surfaces, revealing a gradual density depletion without vapor layer formation and relating surface transition behaviors to the Ising model.

Contribution

It provides simulation-based insights into the phase transition behavior of water in hydrophobic nanopores, connecting surface phenomena to critical transition models.

Findings

Density depletion near hydrophobic surfaces without vapor layer formation.

Order parameter follows a power law with an exponent close to 0.82.

Surface transition behavior aligns with the ordinary transition in the Ising model.

Abstract

The liquid-vapour phase transition near a weakly attractive surface is studied by simulations of the coexistence curves of water in hydrophobic pores. There is a pronounced gradual density depletion of the liquid phase near the surface without any trend to the formation of a vapour layer below the bulk critical temperature Tc. The temperature dependence of the order parameter in the surface layer follows the power law (rol - rov) ~ (1 - T/Tc)^beta1 with a value of the exponent beta1 close to the critical exponent beta1 = 0.82 of the ordinary transition in the Ising model. The order parameter profiles in the subcritical region are consistent with the behaviour of an ordinary transition and their temperature evolution is governed by the bulk correlation length. Density profiles of water at supercritical temperatures are consistent with the behaviour of the normal transition caused by the preferential adsorption of voids. The relation between normal and ordinary transitions in the Ising model and in fluids is discussed.