The Effect of a Limited System Volume on Surface Tensions in a Vapor–Liquid–Solid System

Abstract

Using the lattice gas model, we consider a unified description of three types of two-phase interfaces (vapor–liquid, solid–vapor, and solid–liquid) in the vapor–liquid meniscus system inside a size-limited pore in the form of a rectangular parallelepiped. Pore walls are considered to be undeformable. They form the external field for a stratifying fluid. The state of coexisting “vapor in a pore” and “fluid in a pore” phases satisfy the equality of chemical potentials, which excludes the appearance of metastable states. We present a calculation procedure for molecular distributions and shapes of menisci in the isolated pore considered, which enables the equally accurate calculation of molecular distributions in heterogeneous distributed models of transition regions of three interfaces. The calculation procedure of the surface tension (ST) on three types of two-phase interfaces of the liquid–vapor–solid wall system is elaborated. The procedure of introducing a contact angle in the liquid–vapor–solid pore wall system is described using adsorbate molecular distributions in the considered pore. It is obtained that, as the system decreases, the critical temperature lowers, while the pressure, chemical potential, and ST values of a fluid with a solid increase. Liquid–vapor ST decreases with decreasing area of pore bases (i.e., with pore narrowing), and when the pore height increases, liquid–vapor ST increases. The dependences of the liquid–vapor transition region width and the contact angle of the vapor–liquid meniscus are derived as functions on the pore width and the pore wall potential.