Three Types of Two-Phase Surface Tensions of Stratifying Vapor and Fluid inside a Slit-Like Pore

Abstract

Three types of two-phase interfaces (vapor–liquid, solid–vapor, and solid–liquid) are considered in a liquid–vapor meniscus system inside a slit-like pore. A unified description of these interface surfaces is given on the basis of the lattice gas model, ensuring a uniformly accurate calculation of molecular distributions in heterogeneous distributed models of the transitional regions of interfaces. It is shown that undeformable pore walls generate an external field, affecting the molecular distribution and forming adsorption films due to the potential of adsorbate–adsorbent interaction. Ways of calculating surface tension (ST) via the excess free energy of the interface (according to Gibbs) on the three given two-phase interfaces are discussed, along with means that consider specific features of the nonequilibrium state of a solid. It is established that the state of coexisting vapor-in-a-pore and fluid-in-a-pore phases must satisfy the equality of the chemical potential that excludes the emergence of metastable states. Vapor–solid and liquid–solid STs outside the region of three-phase contact are calculated for the first time, along with local values of a vapor–liquid ST as a function of the removal of a local part of the boundary from the pore walls. It is found that in the center of a pore, the solid–liquid ST is an order of magnitude greater than the liquid–vapor ST, and the solid–vapor ST is two orders of magnitude greater than this value. Local values of a vapor–liquid ST change nonmonotonically as they move away from a wall.