Phase behavior and microstructures of the Gemini (12-3-12,2Br−)–SDS–H2O ternary

Phase behavior and microstructures have been investigated for aqueous mixtures of cationic Gemini surfactant (12-3-12,2Br−) and anionic surfactant sodium dodecyl sulfate (SDS) using freeze-etching and negative-staining and with transmission electron microscopy (TEM). The phase diagram shows different regions characterized by different microstructures. Most of the regions are occupied by multi-lamellar phases in which vesicles coexist with micelles when the solutions are dilute. The multi-lamellar vesicles have higher stability because of their special structures. The ratio of vesicles to micelles varies with concentration and composition of the mixed-surfactant solutions. At higher surfactant concentrations, we observe other phases: the lamellar phase, anisotropic phase, aqueous two-phase system (ATPS), rod-like micelle phase, as well as other unique microstructures such as cylindrical micelles formed by short rod-like micelles, and porous morphology. Observations are reported for the transformation among different phases, especially from rod-like to spherical micelles.