Mixed micellization of cationic/anionic amino acid surfactants: Synergistic effect of sodium lauroyl glutamate and alkyl tri-methyl ammonium chloride

Abstract

In the cleaning field of the cosmetics industry, amino acid surfactants with low irritation and degradability have attracted more and more attention. However, in the actual application system, the amino acid type surfactant has the application difficulty that is not easy to thicken. In this study, the surface activities and application of the surfactant mixtures containing the cationic surfactant dodecyl tri-methyl ammonium chloride (DTAC) and anionic amino acid surfactant sodium lauroyl glutamate (SLG) (cationic/anionic amino acid surfactant system) were systematically studied, which will provide theoretical guidance for practical applications. First, the surface tension of the cationic/anionic amino acid surfactant system was measured, and the CMC value, interaction parameters, Gibbs free energy and other data were obtained. From this, the behavior characteristics of the adsorption and aggregation of SLG and DTAC in the solution can be judged. Then through dynamic light scattering instrument, rheometer, polarizing microscope, etc., we analyze the phase behavior of the cationic/anionic amino acid surfactant system under different compound ratios and different concentrations, and draw a pseudo-ternary phase diagram. Finally, the influence of the length of the hydrophobic chain of cationic surfactants on the phase behavior of amino acid surfactants was investigated. Experiments have found that the addition of cationic surfactant DTAC can significantly reduce the CMC value of the SLG system, and the CMC changes with the increase of the SLG ratio as follows: first decrease and then increase. The interaction parameters show that DTAC and SLG have a strong interaction. Contrary to the phenomenon of precipitation after the compounding of conventional cationic/anionic surfactants, the compounding of DTAC and SLG increases the solubility, reduces the Krafft point of SLG, and increases the application performance. At the same time, the problem of difficult control of the viscosity of the amino acid surfactant system has also been better solved. DTAC and SLG form a worm-like mixed micelle, which has a higher and controllable viscosity. Finally, it was found that changing the hydrophobic chain length of cationic surfactants has a direct effect on the viscosity of the system.