Study on the properties and self-assembly of fatty alcohol ether carboxylic ester anionic surfactant and cationic surfactant in a mixed system

Abstract

Mixtures of anionic surfactant fatty alcohol ether carboxylate ester (A_12–14EC₉E-Na) and cationic surfactant bis-decylmethylhydroxyethylammonium chloride (DEQ) were studied systematically. Compared with single systems (A_12–14EC₉E-Na or DEQ), a mixed system (A_12–14EC₉E-Na/DEQ) exhibits higher surface activity, better application performances, and more diverse self-assembly behaviors due to the synergistic effects between A_12–14EC₉E-Na and DEQ. The interaction parameters and micelle thermodynamic parameters of A_12–14EC₉E-Na/DEQ mixtures indicate stronger intermolecular interaction in both the mixed micelles and gas/liquid interface, and thermodynamic parameters clarify that the micellization is an enthalpy-driven process. When the mass fraction of DEQ reaches 80% (W_DEQ = 80%), the emulsification effect (whether soybean oil or paraffin oil) is optimal and the foaming performance of the mixed system is the best. In addition, the wetting ability is the finest when W_DEQ = 20%. Interestingly, when the mole fraction of DEQ is 20% (α_DEQ = 20%), vesicles and worm-like micelles (WLMs) are formed at a total solution concentration of 10 mM and 100 mM, respectively.