Surface free energy density, surface tension and surface stress of solid-fluid interfaces

Abstract

This chapter inspects aspects of the capillarity of solid–fluid interfaces, with a focus on phenomena in which the area of the interface is changed, either by adding/removing atoms at the interface, at constant atomic structure, or by changing the interatomic spacing at constant number of atoms. Emphasis is on a phenomenological description and on clarifying definitions for the three relevant capillary terms: firstly, a specific surface excess free energy, secondly, the surface tension, and thirdly, the surface stress. Capillary equations—linking the capillary forces to stresses in the underlying bulk medium—are presented and their consequences for distinguishing between the capillarity in solids as opposed to that in fluids are discussed.