Geometry-induced phase transition in fluids: capillary prewetting

TL;DR

This paper uncovers a new first-order phase transition called capillary prewetting in fluids confined within a pore, using density functional theory to analyze its phase diagram and critical behavior.

Contribution

It introduces the concept of capillary prewetting, a novel phase transition preceding capillary condensation, and maps its behavior to planar wetting phenomena.

Findings

Identification of a new first-order phase transition, capillary prewetting.

Mapping of the phase behavior to planar wetting lines.

Calculation of the critical exponent for adsorption divergence.

Abstract

We report a new first-order phase transition preceding capillary condensation and corresponding to the discontinuous formation of a curved liquid meniscus. Using a mean-field microscopic approach based on the density functional theory we compute the complete phase diagram of a prototypical two-dimensional system exhibiting capillary condensation, namely that of a fluid with long-ranged dispersion intermolecular forces which is spatially confined by a substrate forming a semi-infinite rectangular pore exerting long-ranged dispersion forces on the fluid. In the T-mu plane the phase line of the new transition is tangential to the capillary condensation line at the capillary wetting temperature, Tcw. The surface phase behavior of the system maps to planar wetting with the phase line of the new transition, termed capillary prewetting, mapping to the planar prewetting line. If capillary condensation is approached isothermally with T>Tcw, the meniscus forms at the capping wall and unbinds continuously, making capillary condensation a second-order phenomenon. We compute the corresponding critical exponent for the divergence of adsorption.