Vesicle formation of single-tailed amphiphilic alkyltrimethylammonium bromides in water induced by dehydration-rehydration.

Abstract

We recently found that rough glass surfaces (RGSs) can <i>in situ</i> mediate the micelle-to-vesicle transition in single-component solutions of simple single-tailed amphiphiles (STAs), but only result in a relatively small number of vesicles coexisting with a large number of micelles. In the current work, a dehydration-rehydration (DHRH) method was used to induce the formation of vesicles in the single-component aqueous solutions of alkyltrimethylammonium bromides (C_<i>n</i>TABs, <i>n</i> = 12, 14, and 16), a kind of typical cationic STAs. That is, a C_<i>n</i>TAB micelle solution dropped on smooth glass surfaces (SGSs) was first dried, and the dried C_<i>n</i>TAB aggregates were then rehydrated in a monomer solution of C_<i>n</i>TAB. A large population of vesicles and even pure vesicle (or vesicle-dominated) systems were obtained, indicating that the DHRH process could more effectively induce the formation of STA vesicles than RGS <i>in situ</i> mediation. The so-obtained vesicles were characterized using DLS, FF-/cryo-TEM, AFM, SAXS, and fluorescence techniques, and their stability was determined. In addition, the effects of the conditions of DHRH and the chain length of C_<i>n</i>TABs on the vesicle formation were examined. It was demonstrated that the vesicles can be formed as long as the concentrations of C_<i>n</i>TABs in the rehydrated systems are higher than their critical micelle concentrations. The size and wall thickness of vesicles increase with an increase in chain length. A possible mechanism for the DHRH-induced vesicle formation is proposed: bilayer sheets are formed on SGSs during dehydration, and then detached from the SGSs to form vesicles during rehydration. A highly interdigitated structure of alkyl chains between two leaflets was identified in the bilayers, which probably is the origin of the formation and stability of STA vesicles.