Synergism in cationic surfactant and triton X-100 mixtures: Role of enthalpic interactions and conformation changes

Investigation of fundamental properties of colloidal systems of cationic surfactants is important for practical and theoretical reasons. In this work, the nonideal behavior in cetyltrimethylammonium bromide and Triton X-100 mixtures was studied, during the mixed micelle formation. In order to study the aggregation behavior, excess Gibbs energy (GE), excess enthalpy (HE) and excess entropy (SE) were determined. The thermodynamic parameters were monitored as a function of the molar ratio, at different temperatures (283.15-328.15 K). GE, HE and SE were obtained based on the critical micelle concentration values of investigated mixtures. The results of the study indicate existence of synergism in the surfactant mixtures. The increase of the stability of the mixed micelles (GE < 0) is explained as the result of enthalpic interactions and/or entropy changes during the formation of the aggregates.