PHASE-BEHAVIOR OF SYSTEMS OF POLYACRYLATE AND CATIONIC SURFACTANTS

The phase behavior of aqueous systems of sodium polyacrylate (NaPA) and cationic surfactants of the alkyltrimethylammonium bromide type (C(n)TAB) has been investigated. Phase separation occurs in dilute solution in a certain interval of surfactant concentration and may be suppressed by addition of simple salt. At very low concentrations, the polyacrylate chains can bind a considerable amount of surfactant and remain in solution, whereas at higher NaPA concentrations, phase separation occurs at low degrees of surfactant binding to the polymer. The phase diagram for systems of NaPA and C(n)TAB is of the same type as obtained previously for another polyelectrolyte (sodium hyaluronate, NaHy) and the same cationic surfactants. The higher linear charge density for PA as compared to Hy is reflected in a larger two-phase area for this polymer. Systems of a polycation and an anionic surfactant have also been subject to investigation. The interactions between polyelectrolyte and surfactant are seen to be enhanced in these systems as compared to systems of a polyanion and a cationic surfactant but the main features are the same.