Influences of molecular structure of the cationic surfactant, additives and medium on the micellization of cationic/anionic surfactant mixed systems

Abstract

The mixed micellization of four cationic/anionic surfactant aqueous systems formed by quaternary ammonium bromide surfactants with different molecular structures and sodium dodecylsulfonate (Na+AS−) at 318.15K have been investigated. The dissociated Margules model has been used to model the nonideal mixed micellization. The gemini quaternary ammonium bromide (12-3-122+·2Br−) and Na+AS− aqueous mixed system shows the strongest synergism. The effect of added salt constituted by surfactant counterions on the mixed micellization of the gemini quaternary ammonium surfactant and alkali dodecylsulfonate with various counterions in aqueous solution at 318.15K has been explored. When gemini surfactant is in excess, the specific counterion effect becomes insignificant. Whereas, when alkali dodecylsulfonate is in excess, the counterion effect of K+ is stronger than that of Na+. The effect of 1-propanol on the mixed micellization of the 12-3-122+·2Br−/Na+AS−/H2O system at 318.15K has also been explored. Different from the nonmonotonic behavior of the single ionic surfactants, the critical micelle concentration (cmc) of the mixed systems increases with the increase of the concentration of added 1-propanol in the 1-propanol–water mixed medium.