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

The surface properties and the microaggregates of a sulfonate gemini surfactant 12-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 n(SGS12):n(CTAB) = 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 (D-H) of all surfactant aggregates increases with the increase of temperature from 35 degrees C to 50 degrees C. Especially at n(SGS12):n(CTAB) = 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 n(SGS12):n(CTAB) = 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. (C) 2020 Elsevier B.V. All rights reserved.