Structure of salted-out, solubilized micelles and microemulsions on the perfluorinated anionic surfactant tetraethylammonium perfluorooctyl sulfonatestudied by cryogenic transmission electron microscopy

Tetraethylammonium perfluorooctyl sulfonate (TEAFOS; critical micelle conce ntration, 1 mM), which forms a threadlike micelle in its pure solution, was adopted to study the structure of salted-out, solubilized micelles and mic roemulsions by cryogenic transmission electron microscopy. The concentratio n of the surfactant was kept constant at 60 mM. The micelle solution salted out with LiNO3 provided a surfactant phase in the presence of a clear inte rface. The surfactant phase was studded, being formed of homogeneously disp ersed spherical micelles, and had no obvious threadlike forms. The micelles , which solubilized the maximum amount of perfluorinated oil, were spherica l and had the same size as isolated spherical micelles in pure TEAFOS solut ion. The microemulsions were formed in the presence of perfluorinated alcoh ol as cosurfactant and the particles were rotund even when the concentratio n of the perfluorinated oil was equivalent to that for solubilization and t he sizes increased with increasing oil content. The difference in size betw een the solubilized micelles and microemulsions with the same amount of oil suggested that the oil molecules had been solubilized between palisades of perfluorinated alkyl chains in the micelles and had dissolved in the cores of the microemulsions.