Aggregation behavior of cationic fluorosurfactants in water and salt solutions. A cryoTEM survey

The aggregation behavior of the cationic fluorocarbon surfactants 1,1,2,2-t etrahydroperfluoroalkylpyridinium chloride and 2-hydroxy-1,1,2,3,3-pentahyd roperfluoroalkyldiethylammonium chloride in aqueous solution have been stud ied using cryo-transmission electron microscopy as the main technique. The effects on aggregate structure of factors such as surfactant and salt conce ntration, counterion type, and alkyl chain length were investigated. Simila r to hydrocarbon surfactants the fluorocarbon surfactants Self-assemble int o various aggregates such as micelles, threadlike micelles, vesicles, and o ther lamellar aggregates. A distinctive property of the fluorocarbon surfac tants is their tendency to form structures with little curvature, such as c ylindrical micelles and bilayer structures. Even a very small reduction of the repulsion between the headgroups is sufficient to accomplish a sphere t o rod transition, so that a solution of globular micelles in water is turne d into a highly viscous, sometimes viscoelastic solution on the addition of low concentrations of a simple salt. The differences between the fluorocar bon and hydrocarbon surfactants are discussed.