Quaternary ammonium-based and imidazolium-based gemini surfactants: A comparison study

Gemini surfactants have aroused significant attention since their discovery due to their unique properties that arise from the particular molecular structure. However, the effect of a C=C double bond in the spacer has seldom been considered, and common quaternary ammonium-based gemini surfactants have seldom been compared with imidazolium-based ones. In this work, four gemini surfactants, denoted as 12-4-12, 12-4u-12, C12im-4-C12im, and C12im-4u-C12im were synthesized and characterized, and the effects of C=C double bond in the spacer and hydrophilic headgroup on the fundamental properties were investigated. The results showed that imidazolium-based gemini surfactants (C12im-4-C12im and C12im-4u-C12im) have lower critical micelle concentration (cmc), greater efficiency and effectiveness in reducing surface tension, and superior ability to generate micelles compared to the corresponding quaternary ammonium-based ones, but showed comparatively lower salt resistance, foaming, and antibacterial activity. The introduction of C=C in the spacer further decreased the cmc and the Gibbs free energy of micellization, and enhanced the antibacterial activity, but barely affected interfacial adsorption, the efficiency in reducing surface tension, micelle size, or foaming. None of the four gemini surfactants alone was capable of decreasing the interfacial tension to an ultra-low value. The incorporation of sodium cetanol polyoxyethylene ether carboxylate not only significantly decreased the interfacial tension (<10(-2) mNm(-1)), but also remarkably enhanced the salt resistance capacity up to 80,000 mgL-1. This information may be helpful for designing new gemini surfactants tailored for different potential applications.