Phase Behavior and Rheological Properties of Salt-Free Catanionic TTAOH/DA/H2O System in the Presence of Hydrophilic and Hydrophobic Salts

In the cationic and anionic (catanionic) surfactant mixed system, tetradecyltrimethylammonium hydroxide (TTAOH)/decanoic acid (DA)/H2O, abundant phase behaviors were obtained in the presence of hydrophilic and hydrophobic salts. The microstructures of typical La phases with the different compositions were characterized by the transmission electron microscope (TEM) images. Aqueous double-phase transition induced by addition of hydrophilic salts was observed when the cationic surfactant was in excess. Salt-induced reversible vesicle phases could be obtained when the anionic surfactant was excess, whereas the vesicle phase at lower salinity behaves highly viscoelastic but is much less viscoelastic with high salinity which was demonstrated by measuring their rheological properties. The La phase with the positive membrane charges can be finally transferred into an L-1 phase with added salts. The ion specificity of hydrophilic and hydrophobic salts is discussed, and the order of cations is summarized, which is significant for the further study of the Hofmeister effects on catanionic surfactant mixed systems.