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

Abstract Five quaternary ammonium salt Gemini surfactants 2-hydroxyl-propanediyl-α,ω-bis (alkyldodecyl ammonium chloride) ( n -3(OH)-n, where n represents hydrocarbon chain lengths of 10, 12, 14, 16, and 18) were synthesized and characterized by 1 H NMR. Surface activity, adsorption and aggregation behaviors of these cationic Gemini surfactants were investigated by methods of measuring equilibrium surface tension, dynamic surface tension and transmission electron microscope (TEM). The critical micelle concentration (CMC) decreased with an increase in hydrophobic chain length, while the surface tension at the CMC (γ CMC ) showed little change. With TEM measurements, formations of vesicles in n -3(OH)-n (n = 16, 18) solutions occurred and vesicles dimensions depended on their n values. 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.