Equilibrium and Dynamic Surface Properties of Cationic/Anionic Surfactant Mixtures Based on Carboxylate Gemini Surfactant

The equilibrium and dynamic surface properties of cationic/anionic surfactant mixtures of carboxylate gemini surfactant (CGS12) and quaternary ammonium salts with different alkyl chain lengths were investigated, and the synergistic properties and solubilization capacity toward phenanthrene of these mixtures were evaluated. Results show that all cationic/anionic surfactant mixtures exhibit negative interaction parameters, indicating the strong synergistic effects in the reduction of surface tension and the formation of micelles. When the mixing ratio is 1:1, the surface tension reaches the minimum value. Moreover, as the alkyl chain length increases, the interaction parameters become more negative. In addition, the thermodynamic parameters suggest that the formation of mixed micelles is exothermic with a positive change in entropy. The tendency of dynamic surface tension curves of these mixtures is similar to that of pure CGS12. At the same concentration, these mixtures exhibit a higher adsorption rate than pure surfactants, and a lower adsorption potential barrier than cationic surfactants. However, for the CGS12/stearyltrimethylammonium bromide mixture, the drop rate constant of surface tension is lower than that of either component. Compared with the pure surfactant solutions, the cationic/anionic surfactant mixtures exhibit higher solubilization capacity toward phenanthrene. As the length of the alkyl chain increases, the solubilization capacity of the mixed cationic/anionic surfactant increases.