Functions of fluorosurfactants 1: Surface activities-improved and vesicle formation of the short-tailed chain sulfonate salt mixed with a fluorosurfactant

Surface-activity of a short-tailed chain hydrocarbon surfactant, heptane-1-sulfonic acid sodium salt (C₇SNa), was studied by using surface tension and conductivity measurements, which the surface-activity was improved largely by the addition of small amount of a fluorosurfactant, 1H,1H,2H,2H,3H,3H,4H,4H-heneicosafluorotetradecylpyridinium iodine (HFTPI). The phase behavior and vesicle formation of C-H/C-F surfactant mixtures in aqueous solutions are similar to ones of cationic-anionic surfactant (catanionic) systems. The birefringent, viscoelastic Lα-phase consisting of unilamellar and multilamellar vesicles can be observed, which were determined by freeze-fracture transmission electron microscopy (FF-TEM) images. The rheological properties of Lα-phase samples were measured. ¹H and ¹⁹F NMR spectra were measured to monitor the information of self-assemblies of C₇SNa and HFTPI in L₁-phase (spherical micelles) and Lα-phase (vesicles). The results show that the C-H micelles and C-F micelles form in aqueous solutions individually. In Lα-phase (vesicles), the interaction between anionic hydrocarbon (C₇SNa) and cationic fluorocarbon (HFTPI) surfactants exist due to the strong electric static interaction of opposite charge head groups.