Green Synthesis, Surface Activity, Micellar Aggregation, and Corrosion Inhibition Properties of New Gemini Quaternary Ammonium Surfactants

A new series of gemini quaternary ammonium surfactants containing amide groups with the formula C_nH_2n+1CONH­(CH₂)₂N⁺(CH₃)₂(CH₂)₂ N⁺(CH₃)₂(CH₂)₂NHCOC_nH_2n+1·2CH₃CO₃^– (n = 11, 13, 15, 17) have been synthesized by the using green reagent dimethyl carbonate. The structures of these surfactants were confirmed by Fourier transform infrared spectroscopy, ¹H NMR, ¹³C NMR, and mass spectra. Their surface activities and aggregation properties were investigated by surface tension, conductivity, steady-state fluorescence, dynamic light scattering, and transmission electron microscope measurements. The results show that these synthesized gemini quaternary ammonium surfactants reduce the surface tension of water to a minimum value of 28.21 mN·m^–1 at a concentration of 0.256 mmol·kg^–1 and self-assemble spontaneously into double layer aggregates which are mostly single-room vesicles and multilamellar vesicles. Furthermore, with increasing alkyl chain length, their critical micelle concentration values and the degree of counterion binding (β) decrease; and the spontaneous tendency of vesicle formation and the micellar aggregation numbers (N_m) increase. They are also found to be effective corrosion inhibitors for A3 steel in acid solution.