Enthalpies of mixed-micelle formation
Critical micelle concentrations have been measured for binary mixtures of an anionic and a polyoxyethylenated non-ionic surfactant in aqueous solution. The data were used to calculate the molecular interaction parameter β in the Rubingh theory of mixed-micelle formation. Enthalpies of mixed-micelle formation determined calorimetrically were then compared with theoretical values based on β. Differences found between expected and observed enthalpies are attributed to deficiencies in the theory with respect to the temperature dependence of β and the variation of counterion binding as the micelle composition changes.