MECHANISM OF MICELLE TO VESICLE TRANSITION IN CATIONIC-ANIONIC SURFACTANT MIXTURES

The present paper investigates the cationic-anionic surfactant mixture s with a view to understand the role of polar head packing in bringing about a vesicle to micelle transition. Differences in behavior betwee n addition of sodium dodecylbenzenesulfonate (SDBS) and sodium dodecyl sulfate (SDS) to cetyltrimethyl-ammonium-p-toluenesulfonate (CTAPTS) solutions are investigated by NMR and molecular modeling techniques. I t is concluded that the complex formed between SDS and CTAPTS is more tightly bound than that between SDBS and CTAPTS, leading to precipitat ion rather than vesicle formation in the latter case. Molecular modeli ng shows that the SDBS chain has a bend in the molecule, and this faci litates loose packing of the complex neccessary for the formation of v esicles.