Aggregation properties and mixing behavior of hydrocarbon, fluorocarbon, and hybrid hydrocarbon-fluorocarbon cationic dimeric surfactants

The synthesis, phase behavior, and mixing properties of cationic dimeric (gemini) surfactants having one or two perfluoroalkyl chains is described and compared to that of analogue hydrocarbon surfactants. The combination of the dimeric character of the amphiphiles with the high hydrophobicity of the fluorocarbon chains leads to very low critical micelle concentration values and unusually low characteristic times of exchange between surfactants in the bulk solution and surfactants in the aggregate. This results in slow exchange on the NMR time scale, which allows a practical study of micellization and comicellization by NMR. With respect to the morphology of the aggregates, the fluorocarbon amphiphiles do not simply behave as more hydrophobic amphiphiles. Instead, they assemble into various structures including very stable unilamellar and multilamellar vesicles not seen in their hydrocarbon analogues. The hybrid hydrocarbon-fluorocarbon dimeric surfactant exhibits features of both families. In particular it mixes with either hydrocarbon or fluorocarbon surfactants, whereas the latter two undergo a macroscopic phase separation.