Perforated Vesicles as Intermediate Structures in the Transition from Vesicles to Micelles in Dilute Aqueous Systems Containing Long Chain Alcohols and Ionic Surfactants

Morphologies of aggregates in mixtures of long chain alcohols (n-decanol, n-dodecanol, and oleyl alcohol) and cationic surfactants (cetylpyridinium chloride, cetyltrimethylammonium bromide, and chloride) in dilute aqueous salt solutions were investigated by cryogenic transmission electron microscopy. In all cases elongated micellar structures transformed into vesicles with increasing alcohol concentration. Perforated bilayer structures were clearly identified in systems with oleyl alcohol and CTAB, in particular in 0.100 M NaBr. Increasing the salt concentration to 0.200 M other aggregates dominated composed of threadlike, probably branched, and interconnected micelles. A gradual evolution of morphologies was observed with increasing alcohol content at the lower salt concentration: thread-like micelles (developing branching to some extent), perforated vesicles, coexisting perforated and smooth bilayer structures, only smooth bilayers, and finally also inverted strucutures.