十八烷基二甲基氯化铵水溶液动态表面张力及吸附动力学研究

使用最大气泡法测定了十八烷基二甲基氯化铵（C_(18)DAC）水溶液的动态表 面张力，考察了浓度、温度等对其DST的影响，详细表征了DST随时间的变化过程， 计算了动态表面张力的各种参数（n，t_i，t~*，t_m，R_(1/2)）。结合Word- Tordai方程计算了表观扩散系数（D_a）和吸附势垒（E_a），对其吸附动力学模式 进行了研究，探讨了DST参数的物理意义。结果表明，t~*值越小，吸附势垒E_a越 大，宏观扩散系数D_a越小，表面活性剂分子越不易吸附在溶液表面；C_(18)DAC低 浓度时吸附属于扩散控制模式，高浓度时属于混合控制模式；高浓度时，在吸附初 期（t → 0）为扩散控制模式，吸附后期（t → ∞）为混合控制模式。

Study on the Dynamic Surface Tension and Adsorption Kinetics of C_ (18)DAC

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.