Studies on the surface properties and microaggregates of cationic/anionic surfactant mixtures based on sulfonate gemini surfactant

Abstract

The surface properties and the microaggregates of a sulfonate gemini surfactant 1,2-bis(N-dodecyl-N-propane sulfonate sodium)-ethane (SGS12) and conventional cationic surfactant hexadecyl trimethyl ammonium bromide (CTAB) mixtures were studied. The critical micelle concentration (CMC) values of SGS12, CTAB, and SGS12/CTAB mixtures (1:1) were 0.0045, 0.89 and 0.0031 mmol·dm‐3, respectively. By changing the molar ratios of SGS12 to CTAB, the transitions between micelles and vesicles were observed. When nSGS12:nCTAB = 4:6, the size of surfactant aggregates increased abruptly to 68.06 nm, and a pale blue opalescence appeared, which was consistent with the size and optical characteristics of the vesicles. The hydrodynamic diameter (DH) of all surfactant aggregates increases with the increase of temperature from 35 °C to 50 °C. Especially at nSGS12:nCTAB = 6:4, we observed a temperature-induced transition from micelles to vesicles. We also investigated the effects of 1-propanol on the SGS12/CTAB precipitate. At nSGS12:nCTAB = 4:6, the addition of 1-propanol led to the precipitate → vesicles → micelles transition. Moreover, the addition of NaCl increased the aggregate size of the SGS12/CTAB mixtures, and we observed the light blue opalescence. The addition of NaCl induced the formation of vesicles. As a result, the SGS12/CTAB mixtures have more excellent surface activity than either component. By changing the composition, temperature, the concentration of salt, and the volume fraction of alcohol, the transition of precipitation → vesicles → micelles can be achieved.