Synergistic Properties of a Mixed Micelle System Consisting of a Nonionic Fluorinated Surfactant and a Cationic Surfactant

Abstract The physicochemical properties of aqueous surfactant mixtures containing a nonionic fluorosurfactant (undecafluoro- n -pentyldecaoxyethylene ether (C 5 F 11 EO 10 )) and various amounts of a cationic surfactant (decyltrimethylammonium bromide (DeTAB)) were determined by surface tension and conductivity measurements. All values of the critical micelle concentrations of the mixtures turn out to be smaller than those of both pure surfactants revealing the presence of a significant synergy for all DeTAB proportions in the mixed system. The analysis of the experimental data was performed on the basis of three different well established thermodynamic models of mixed micelle formation to determine several relevant parameters, especially the micelle composition, the interaction parameters, and the free energy of micelle formation. The results indicate that the dominant interactions between DeTAB and C 5 F 11 EO 10 molecules are attractive. The main reason for this behavior could be attributed to the complexation between the polyoxyethylene chain of C 5 F 11 EO 10 and the quaternary ammonium group of DeTAB giving rise to stable structures.