Equilibrium and dynamic surface properties of long-chain quaternary ammonium hydroxides with different chain length and number

Abstract

ABSTRACTThe equilibrium and dynamic surface tensions of five long-chain alkyl ammonium hydroxides (AAH) at the air/aqueous solution interface were investigated, and the effects of the length and number of alkyl chain on surface tensions had been discussed. With the increase of the length, the equilibrium surface tension (EST) increased from 28.65 to 40.52 mN/m. While, for the double chains at the critical micelle concentration (CMC), the EST decreased from 32.71 to 26.61 mN/m with the length increasing. In addition, the adsorption behaviors of the AAH were analyzed and the effective diffusion coefficients (Deff) were calculated on basis of the Ward–Tordai equation. Moreover, the time required to attain the EST decreases with the increase of surfactant concentration. The longer the C–H chain is, the lower surface tension at initial concentration is. What’s more, the diffusion processing of the AAH to air/water interface mainly depends on the surfactant concentration, and the adsorption is controlled by diffusion mechanism in a dilute concentration, while under a high concentration the adsorption is controlled by mixed diffusion–kinetic mechanism.