Disjoining pressure in vapor layers near planar and spherical lyophobic surfaces

Abstract

A classical square-gradient density functional theory is used for describing disjoining pressure in vapor layers between a lyophobic planar smooth solid substrate and stable bulk liquid, and between a lyophobic nanosized solid sphere and stretched bulk liquid. Profiles of local density, of normal and tangential components of the local pressure tensor in the interlayers are calculated and analyzed for planar substrate and spherical particle at several values of the chemical potential of the fluid and parameters controlling wettability of solid. The pressure tensor is found to be significantly anisotropic in the vapor layers near the smooth solid surfaces. Mechanical and thermodynamic definitions of the disjoining pressure in the spherical vapor layer were compared and shown to be consistent. In contrast to case of liquid films, the disjoining pressure in vapor layers near the nanosized lyophobic solid particle is found to be greater than near the planar wall. It has been directly shown that, depending on lyophobicity, the disjoining pressure isotherms change from nonmonotonic to monotonic functions of the vapor layer thickness.