Salt Effects on Aqueous Cationic/Anionic Surfactant Two‐Phase Regions

The influence of added salts (KCl, NaF, NaCl, NaBr, Na2SO4, Na3PO4) on aqueous cetyltrimethylammonium bromide (CTAB)/sodium dodecyl sulfonate (AS) two‐phase regions were studied. For KCl, the concentration dependence of salt effect on aqueous two‐phase regions was investigated. When brine substitutes pure water as a solvent, the positions of aqueous two‐phase regions in the phase diagram change. The results indicate that for aqueous two‐phase systems with excess anionic surfactant (ATPS‐A), the salt effect was mainly dependent on the cationic inorganic counterions, whereas for aqueous two‐phase systems with excess cationic surfactant (ATPS‐C), the salt effect was mainly dependent on the anionic inorganic counterions. The shift of aqueous two‐phase region is strengthened following the Hofmeister series. All the experiments were performed at 318.15 K.