Equilibrium and dynamic surface tension properties of Gemini quaternary ammonium salt surfactants with ester groups

Two series of quaternary ammonium salt Gemini surfactants with ester groups (n-m-n, where n represents hydrocarbon chain lengths of 10, 12, 14 and 16, m represents spacer group lengths of 2 and 6) were synthesized and characterized by H-1 NMR. Surface activity and adsorption of these cationic Gemini surfactants were investigated by methods of measuring equilibrium surface tension and dynamic surface tension. The critical micelle concentration (CMC) decreased with an increase in chain length, while increased with the length of spacer group. Moreover, data obtained were analyzed in accordance with Word-Tordai equation, and the diffusion coefficients for ionic liquid molecular adsorption in the initial stage and final stage under different concentration were figured out respectively. The results indicated that the adsorption process was controlled by a diffusion step at low surfactant concentration while by a mixed kinetic-diffusion adsorption mechanism at high surfactant concentration. (C) 2016 Elsevier B.V. All rights reserved.