Salt effects on the surface tensions of dilute electrolyte solutions: The influence of nonzero relative solubility of the salt between the coexisting phases

Publisher Website
Google Scholar
Abstract
Extant theories of salt effects on the surface tensions of dilute fluid electrolyte solutions explicitly assume that the solubility of the salt in one of the coexisting phases is negligible. It is shown here that this assumption can influence both the sign and the analytical form of the dependence of the surface tension on the salt concentration in the limit of low concentrations. The variability of the low concentration behavior of the surface tension is traced to short ranged ion–solvent interactions involved in determining the relative solubility of the salt in the two coexisting phases. In particular, if there is appreciable solubility of the salt in both phases, and if the short ranged ion–solvent forces are dissimilar, then we predict that the surface tension should decrease proportional to the square root of the salt concentration ρ1/2 in the limiting region of low concentrations. This is contrasted to the ρ ln ρ limiting law which results when the solubility in one of the phases is vanishingly small.