Miscibility of sodium chloride and ionic surfactant in adsorbed film and aggregate

The adsorption, micelle formation, and salting-out of dodecylammonium chloride in the presence of NaCl were studied from the viewpoint of mixed adsorption and aggregate formation. The surface tension of aqueous solutions of a NaCl–dodecylammonium chloride mixture was measured as a function of the total molality and composition of the mixture. Judging from phase diagrams of mixed adsorption and aggregate formation, NaCl and dodecylammonium chloride are miscible in the adsorbed film and coagel particle at high NaCl concentrations due to specific (nonelectrostatic) interaction between dodecylamonium ion and the counterion, while they are immiscible in the micelle. The difference in miscibility among the oriented states was ascribed to the difference in geometry among the states and to the interaction between bilayers in a coagel particle. Miscibility and specific interaction are compared between the mixtures of NaCl with dodecylammonium chloride and sodium dodecylsulfate.