Solute-solvent interactions interfacial tension

The advantage of using interfacial tension as a measure of solute-solvent interactions is that it can be measured for substances whose intermolecular forces are quite different from each other. Thus, it is useful for estimating solubilities for systems that are highly irregular. In contrast, regular solution approaches are useful when solute and solvent polarities are similar and the interfacial tensions are immeasurable. 

The introduction of the interfacial tension into the cavity term was first done by Y alkowsky et al., who also argue that a separate solute-solvent interaction term is unneeded, as the solute-solvent interaction is already embodied in the interfacial tension. In our theory we explicitly show the coupling between the solute-solvent and solvent-solvent interactions (eq. [5.5.19]), but this is in addition to the solute-solvent interaction (eq. [5.5.13]). This difference between the two theories is a subtle issue that requires clarification. 

The terms between the brackets correspond to the osmotic contribution to the Gibbs free energy (AG), and they also constitute the standard expression for AG of the Flory-Huggins theory of polymer solutions [61], where < p is the volume fraction of polymer and the ratio of the equivalent number of molecular segments of solvent to polymer (usually expressed as the ratio of molar volumes of solvent and polymer). Xap is the Flory-Huggins interaction parameter of solvent and polymer and the last term of Equation 14.1 is the interfacial free energy contribution where y is the interfacial tension, the molar volume of solvent, and r the particle radius. T is temperature in Kelvin and R is the universal gas constant. 

The extent of adsorption depends not only on the relative energies of interaction of the solute (2) and solvent (1) with the surface, represented by the difference (o-f — erf) between the interfacial tensions, but also by the deviations of the bulk and surface regions from ideality. In a second paper the... 

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