ENHANCED AMPHIPHILE ADSORPTION AT LIQUID-LIQUID INTERFACES IN A MICELLAR SOLUTION MODEL

We analyze in mean-field approximation the liquid-liquid interfacial p roperties of a micellar solution model designed to describe amphiphile s in polar solvents. Under specific conditions the amphiphile concentr ation profiles become non-monotonous and entail enhanced interfacial a dsorption. We find that this behavior is related to the occurrence of asymmetry of the closed-loop coexistence curve for dilute and concentr ated micellar liquids above a lower critical solution temperature T-c. We obtain quantitative agreement with ellipsometric studies of partia lly miscible mixtures of non-ionic amphiphiles in water. The model all ows for elimination of the degrees of freedom within the aggregates, a nd this leads to an equivalence with the ordinary Ising model but with temperature and concentration dependent field and coupling. The latte r is identified with the effective intermicellar interaction. (C) 1998 Elsevier Science B.V. All rights reserved.