Bulk-to-surface distribution coefficients and surface activity coefficients from surface tension measurements

Abstract

The equations which relate component bulk-to-surface distribution coefficients and surface activity coefficients to bulk composition, partial molal areas, and surface tension are derived for binary liquid systems from fundamental thermodynamic considerations. The derived relations for bulk-to-surface distribution coefficients and surface activity coefficients apply equally well to both components of the binary systems, and they are valid throughout the entire range of concentrations for simple binary liquid systems. The bulk-to-surface distribution coefficient and surface activity coefficient values are used to identify the capillary active components of binary systems. Also, the limiting values for these parameters and their temperature dependence may be used to establish standard state values for desorption free energies, enthalpies, and entropies for both components of a binary system. The application of the derived relations to several simple binary liquid solutions of organic compounds is considered, the capillary active components are identified, and the variations of bulk-to-surface distribution coefficients and surface activity coefficients with composition are illustrated.