Phase behavior and densities of aqueous two-phase systems formed by 1,3-propanediyl bis(dodecyl dimethylammonium bromide) and sodium dodecyl sulfonate mixtures

Phase behavior of aqueous mixed surfactants, 1,3-propanediyl bis(dodecyl dimethylammonium bromide) and sodium dodecyl sulfonate, has been studied at 318.15 K. The influence of added sodium halides (NaF, NaCl, and NaBr) has been investigated. For those systems studied, only one aqueous two-phase region is formed in which cationic gemini surfactant is in excess. Different salt effects on the densities of the concentrated phases in aqueous two-phase systems were observed for the three sodium halides. Density experiments indicate that contributions of various ions and water to the density of the solutions are near additive. Whether the concentrated phases in aqueous two-phase systems are the bottom phases with higher densities or not are dependent on the different counterion binding ability and on the different contribution to the density of the three halides.