Phase equilibrium with a two-phase system with surface area

The consideration of a surface in a thermodynamic system entails the incorporation of an additional force field, beyond the intermolecular interactions, generated by the anisotropy of the surface. Therefore, the chemical potential of the surface does not have the same information as the chemical potential of a volumetric phase. In this regard, two criteria have been used when contemplating phase equilibrium, one where a term encompassing anisotropy is added and the other where it is not. This paper presents the development of both and offers a view where both criteria can be made equivalent in terms of the information contained in the activity coefficients used in the description of chemical potentials. As a consequence of this derivation a surface–volume partition coefficient is calculated based only on volumetric properties corrected for the anisotropic force field.