A MODIFIED SEMIEQUILIBRIUM DIALYSIS METHOD FOR STUDYING SOLUBILIZATION IN SURFACTANT MICELLES - TESTING THE SEMIEQUILIBRIUM ASSUMPTION

The detailed analysis of data obtained with the semiequilibrium dialysis (SED) method for studying solubilization in surfactant micelles requires accounting for the formation of micelles in the permeate compartment and for the presence of solubilized organic solute in these micelles. An extension of the SED method is proposed here, in which the concentration of surfactant is maintained well above the critical micelle concentration (cmc) in both compartments of the dialysis cell. Under these conditions, it is shown that the validity of the ''semiequilibrium'' assumption, viz., that the organic solute reaches equilibrium simultaneously with both surfactant solutions, can be demonstrated for solutions of small organic molecules and typical ionic surfactants. Agreement of the new results with those obtained in conventional SED results (obtained using a concentrated surfactant solution on one side of the dialysis membrane and pure water on the other) implies that semiequilibrium is ordinarily attained in SED studies of low molecular weight solutes such as phenol and its derivatives. It is also suggested that the new modification of the SED method has important mathematical and experimental advantages over conventional SED in inferring equilibrium solubilization results.