Phase Distribution in Solid-Liquid-Vapor Systems

Abstract

Spatial distribution of phases in a solid-liquid-vapor system are described by the classical Young’s equation¹

$${\gamma _{sv}} - {\gamma _{s\ell }} = {\gamma _{\ell v}}\cos \theta ,$$

((1))

where γ is the interfacial tension between solid-vapor (sv), solid-liquid (sl), and liquid-vapor (lv) phases, γ_sv-γ_sl is the driving force for wetting, and θ is the contact angle at a solid-liquid-vapor triple point as measured through the liquid phase. Furthermore, in systems where the solid phase is polycrystalline

$${\gamma _{ss}} = 2{\gamma _{sf}}\cos \frac{\Phi }{2},$$

((2))

where γ_ss is the interfacial tension at the solid-solid grain boundary, γ_sf is either γ_sl or γ_sv, and Φ is the dihedral angle² at a solid-fluid-solid triple point measured through the fluid phase. Both of these equations have been extensively used in various fields to describe the conditions of mechanical equilibrium of a capillary system under chemical non-equilibrium conditions, without explicitly considering the effect of chemical reactions on the interfacial tensions. Recently, it has been shown³ that an interfacial reaction or diffusion of a component from one bulk phase to the other across an interface results in a transient decrease in the corresponding interfacial tension by an amount equal to the free energy of the effective chemical reaction per unit area at that interface.