INTERACTION OF ALKYLTRIMETHYLAMMONIUM SURFACTANTS WITH POLYACRYLATE AND POLY(STYRENESULFONATE) IN AQUEOUS-SOLUTION - PHASE-BEHAVIOR AND SURFACTANT AGGREGATION NUMBERS

The interactions between polyacrylate and cationic surfactants has been studied. Aggregation numbers of dodecyltrimethylammonium (DoTA+) micelles formed in very dilute aqueous solutions of polyacrylate have been estimated with time-resolved fluorescence quenching, using as quencher dodecylpyridinium ion, which is distributed similar to DoTA+ between micelle and water subphases. The aggregation numbers (=65) were found to be the same as in 50 mM dodecyltrimethylammonium bromide (DoTAB) solutions. The distribution of the quencher between micelles and water was also investigated. It was concluded that the quencher and the surfactant mixed ideally in the micelles. The effect of salt on the phase behavior in aqueous solutions of polyacrylate together with DoTAB, dodecyltrimethylammonium chloride (DoTAC), cetyltrimethylammonium bromide (CTAB), or cetyltrimethylammonium chloride (CTAC) has been investigated. The concentration of surfactant and the aggregation number in both of the coexisting phases in the two-phase region of the phase diagram were estimated. The aggregation numbers (about the same in dilute and concentrated phases) for DoTAB, DoTAC, and CTAC, were approximately 80, 70, and 150, respectively. CTAB formed rodlike micelles in all investigated phases. We found that both the choice of salt and the size of the micelles were important for the extension of the two-phase region. Sodium polyacrylate-CTAB showed a segregative phase behavior at high concentrations of salt. The phase behavior of the system sodium poly(styrenesulfonate)-DoTAB-water was also investigated. The system was found to behave differently in many respects from the system with polyacrylate and the same surfactant. The critical aggregation concentration in dilute solutions of PSS was estimated from surfactant selective electrode measurements and was found to increase with the concentration of the polyelectrolyte. Phase separation started at the same PSS-DoTAB ratio (almost-equal-to 1) in both dilute and concentrated solutions.