Surface layers overlap and effective adhesion in reverse micelles: A discussion from the adhesive spheres mixture model

Structural data on reverse micelles from the literature are analyzed from the adhesive spheres mixture model in the Percus-Yevick approximation. The solvent is modeled by a fluid of pseudoadhesive spheres with same compressibility and coordination number as a square well fluid. The attractive part of the direct intermicellar potential is taken proportional to the overlap volume of interpenetrating surface layers. The micelle-solvent coupling is characterized by a square or triangular well and a constraint on the packing fractions. A very good correlation is then found between the micelles stickiness parameters computed from the actual potentials via the equality of second virial coefficients and those determined from a fit to experiment. The change in effective adhesion observed with micelles of different surface composition and in the same solvent can then be associated to the change in the direct intermicellar interaction at nearly unchanged solvent-micelle interactions. The interpretation of the role of tho overlap volume resulting from this multicomponent approach is contrasted with that based on approximate calculations of the potential of mean force. (C) 1997 American Institute of Physics.