The dynamic surface tension (DST) of octadecyl dimethylammonium chloride (C_(18)DAC) was measured using the maximum bubble pressure method. The effects of C_(18)DAC concentration and temperature on DST have been investigated systematically, and the parameters (n, t_i, t~*, t_m, γ_m, R_(1/2)) have also been calculated out. Combined with Word- Tordai equation, the effective diffusion coefficient D_a and the adsorption barrier E_a were obtained. The adsorption kinetics was studied and the physical meaning of DST parameters was also discussed. The results show that the smaller the t~*, the smaller the effective diffusion coefficient D_a, the bigger the adsorption barrier, and the more difficult for the surfactant to adsorb on the solution surface. The adsorption process is controlled by a diffusion step at low surfactant concentration or controlled by a mixed kinetic-diffusion adsorption mechanism at high surfactant concentration. When the concentration is high, the adsorption process is controlled by a diffusion step at the beginning; toward the end, it changes to a mixed kinetic-diffusion adsorption mechanism.

Key words: SURFACE TENSION, ADSORPTION, QUATERNARY AMMONIUM COMPOUNDS, DIFFUSION COEFFICIENTS, KINETIC STUDY