Enhanced amphiphile adsorption at liquid–liquid interfaces in a micellar solution model

We analyze in mean-field approximation the liquid–liquid interfacial properties of a micellar solution model designed to describe amphiphiles in polar solvents. Under specific conditions the amphiphile concentration profiles become non-monotonous and entail enhanced interfacial adsorption. We find that this behavior is related to the occurrence of asymmetry of the closed-loop coexistence curve for dilute and concentrated micellar liquids above a lower critical solution temperature Tc. We obtain quantitative agreement with ellipsometric studies of partially miscible mixtures of non-ionic amphiphiles in water. 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.