Synergistic effects of Gemini cationic surfactants with multiple quaternary ammonium groups and anionic surfactants with long EO chains in the mixed systems

Abstract

In this study, two different anionic surfactants containing long polyoxyethylene chains involving sodium fatty alcohol ether carboxylates (AE9C) as well as isomeric sodium fatty alcohol ether sulfates (iso-AE9S) are mixed with a new Gemini cationic surfactant bearing four quaternary ammonium groups (TC-GS). Then, the surface properties and aggregation behavior of the two mixed systems were investigated. The effect of the long polyoxyethylene chains on the conformation and hydration of the hydrophilic head group of AE9C and iso-AE9S weakened their negative charge density, thus hindering their excessive electrostatic adsorption with TC-GS and improving the stability of the mixed systems. The positive synergistic effects of TC-GS/AE9C and TC-GS/iso-AE9S exhibited significantly lower critical micelle concentration, faster diffusion rates, and superior wetting capability compared to single surfactants. The micellization process of both mixed systems is spontaneously enthalpy-driven, and the diffusion-adsorption process is consistent with the mixed diffusion-kinetic mechanism. Finally, both mixed systems are capable of forming complex and interesting aggregate morphologies, with TC-GS/AE9C can form multilayer spherical vesicles and TC-GS/iso-AE9S can form multicompartment concentric spherical vesicles.