The High-Concentration Stable Phase: the Breakthrough of Catanionic Surfactant Aqueous System

Precipitates occur readily in the aqueous mixture of cationic and anionic surfactants. We report that the precipitates formed in the catanionic surfactant systems at charge ratios deviated from 1:1 can be solubilized by simply increasing the total surfactant concentrations. At higher concentrations, there are vesicles in the supernatant, which will sequester the monomer surfactant in equilibrium with the precipitates. This shifts precipitation-solvation equilibrium continuously. As a result, the precipitates vanish when all the surfactants in the precipitates are taken into the vesicles. In this way, a high-concentration stable phase (HCSP) can be formed in the precipitated surfactant systems, which can be generalized to all catanionic surfactant systems. We envision the concentration-triggered HCSP is very promising in guiding the large-scale application of catanionic surfactants.