On the Thermodynamics of Solubilization

The thermodynamic theory of solubilization has been formulated with introducing the notion of standard solubilization affinity. An important component of this notion is the Laplace capillary pressure represented in the phase interpretation of the hydrocarbon core of a normal micelle. The partition coefficient of a solubilisate is also interpreted both in terms of a mole fraction within the formalism of chemical thermodynamics and in terms of concentration within the formalism of statistical mechanics. In contrast to the widespread approach using fictitious micellar “pseudophase,” this interpretation is based on the real physical picture of solubilisate partition between micelles and an ambient solution. Moreover, an exact solution has been presented for the problem of the effect of solubilization on the value of the critical micelle concentration (CMC). The consideration is based on the mass action law and new methods of defining the CMC via the constant of this law, aggregation number, and solubilisate concentration. The cases of solubilization from saturated (when studying solubility) and unsaturated (with an arbitrary concentration) solutions have been analyzed. However, the same result has been obtained in all variants, namely, solubilization decreases the CMC.