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 (g emini) surfactants having one or two perfluoroalkyl chains is described and compared to that of analogue hydrocarbon surfactants. The combination of t he dimeric character of the amphiphiles with the high hydrophobicity of the fluorocarbon chains leads to very low critical micelle concentration value s and unusually low characteristic times of exchange between surfactants in the bulk solution and surfactants in the aggregate. This results in slow e xchange on the NMR time scale, which allows a practical study of micellizat ion and comicellization by NMR. With respect to the morphology of the aggre gates, the fluorocarbon amphiphiles do not simply behave as more hydrophobi c amphiphiles. Instead, they assemble into various structures including ver y stable unilamellar and multilamellar vesicles not seen in their hydrocarb on analogues. The hybrid hydrocarbon-fluorocarbon dimeric surfactant exhibi ts features of both families. In particular it mixes with either hydrocarbo n or fluorocarbon surfactants, whereas the latter two undergo a macroscopic phase separation.