Interfacial and capillary properties of a micellar solution model

A prominent feature of the phase behavior of aqueous solutions of nonionic amphiphiles is a phase separation into dilute and concentrated micellar liquids above a lower critical solution temperature Tc. Experiment has revealed a strong asymmetry of the coexistence curve, a high sensitivity of the (effective) critical indexes on deviations of the critical composition, and an unusual excess adsorption at the liquid-liquid interface as indicated by ellipsometric measurements. Here, we review and extend the study of a micellar solution model designed to describe amphiphiles in polar solvents and, as we illustrate, it reproduces the properties mentioned above. The model allows for elimination of the degrees of freedom within the aggregates, and this leads to an equivalence with the ordinary Ising model but with temperature and concentration-dependent field and coupling. The latter is identified with the effective intermicellar interaction.