Effects of polyelectrolytes on the structures and interactions of surfactant aggregates

Aqueous solutions of sodium polyacrylate (NaPA) have been mixed with different phases of the system water-cetyltrimethylammonium bromide (CTABr). In all mixtures, the surfactant ions (CTA(+)) associate to form micelles. The polyions (PA(-)) bind to these micelles, displace their counterions, and bridge them together. The replacement of micellar counterions changes the micellar shapes. The bridging may change the distances between micelles, and cause them to separate into a concentrated phase; in this case excess water and salt are released in a dilute aqueous phase. The structures of the concentrated phases have been determined. At low water contents, the hexagonal, nematic, and micellar phases of the polymer-containing system merge with the corresponding phases of CTABr/water. At high water content, the concentrated phases that separate are closer to the hexagonal and cubic phases of cetyltrimethylammonium acetate/water.