On the thermodynamic relations between immersional and adhesional wetting

A thermodynamic analysis of adsorption from a single-component fluid, either vapor or liquid, on the surface of a single-component solid is systematically developed. The analysis is based on the Gibbsian treatment of surface regions and assumes only that the interfaces are planar, that the solid and fluid phases are mutually insoluble, and that the solid is inert. The treatment is then applied to the interpretation of adhesional wetting (contact angle) and immersional wetting (heat of wetting) measurements. A relationship between the quantities obtained from these two types of wetting measurements is derived. This relationship is of the GibbsHelmholtz form and involves the dependence of the contact angle on temperature. Problems which arise in a proposed experimental test of the relationship are discussed.