Self-Assembly of Cationic/Anionic Surfactants with Highly Dissymmetric Lengths of Alkyl Tails

By introducing a new method of solution preparation, systems of equimolar mixing cationic/anionic surfactants with dissymmetric lengths of alkyl tails were investigated using light scattering, rheology, and freezing-fracture transmission electron microscopy (FF-TEM) measurements, in which the cation was docosyltrimethylammobium bromide (C22TABr) and the anions were sodium alkylcarboxylates (Cn-1COONa, n = 4, 6, 8, 10, 12, 14, 16). The results showed that spherical micelles were favored when the cationic/anionic surfactants had highly dissymmetric length tails (C22/n4). With decreasing dissymmetry of the alkyl tail lengths, the aggregates transformed to rod-like micelles, worm-like micelles, and finally vesicles. In the vesicle-formed cases, the size of the aggregate considerably increased with decreasing dissymmetry of the alkyl tail lengths. By analyzing the mechanism of aggregation, the geometry of the cation/anion pair is thought to determine the morphology and the transition of aggregates.