PHASE-BEHAVIOR IN MIXTURES OF CATIONIC AND ANIONIC SURFACTANTS IN AQUEOUS-SOLUTIONS

Phase behavior of cationic/anionic surfactant mixtures of the same cha in length (n = 10, 12 or 14) strongly depends on the molar ratio and a ctual concentration of the surfactants. Precipitation of catanionic su rfactant and mixed micelles formation are observed over the concentrat ion range investigated. Coacervate and liquid crystals are found to co exist in the transition region from crystalline catanionic surfactant to mixed micelles. The addition of oppositely charged surfactant dimin ishes the surface charge density at the mixed micelle/solution interfa ce and enhances the apparent degree of counterion dissociation from mi xed micelles. Cationic surfactants have a greater tendency to be incor porated in mixed micelles than anionic ones.