Kinetic studies on adsorption and desorption of surfactants

采用停流法研究了表面活性剂离子在固液界面的脱附动力学。用铂电极对停流分光光度计的混合池进行了改进，使之用于电导检测。通过记忆记录系统监测解吸过程中电导率随时间的变化。所用表面活性剂为烷基硫酸钠（C_<10>-C_<16>）。在低于cmc的浓度下，表面活性剂离子从尼龙粒子上的解吸速率与表面活性剂浓度无关，速率常数由一级反应方程求得，由不同温度下分散在表面活性剂水溶液中的粒子的电动势求得了表面活性剂在尼龙粒子上的平衡吸附等温线.吸附平衡常数K和饱和吸附量Ts由Langmuir图确定。K和Ts的值获得 ...更多信息 并与电导法进行了比较。两者的K值基本一致。Ts值的差异提供了关于滑移面和吸附表面活性剂解离度的信息。吸附速率常数由解吸速率和平衡常数估计，假设二级动力学。测定了脱附速率常数在1 - 6秒~ 2范围内，吸附<-1>速率常数在2 - 8 × 10 ~ 4 mol·dm ~（-3）秒~ 2范围内，脱附速率常数<-1><-1>随烷基链上碳原子数的增加而减小，吸附速率常数随烷基链上碳原子数的增加而增大。由Arrhenius图计算出脱附活化能为65.5kJ/mol，与同一体系的吸附焓值基本一致。少

The desorption kinetics of surfactant ions at solid/liquid interfaces was investigated by applying the stopped-flow method. A mixing cell of stopped-flow spectrophotometer was modified with platinum electrodes for electric conductivity detection. The change in electric conductivity with time in the desorption process was monitored by a memory-recorder system. Surfactants used were sodium alkyl sultates (C_<10>-C_<16>). The desorption rate of surfactat ions from nylon particles was independent of the surfactant concentration and the rate constants were obtained by applying the first-order reaction scheme, at the concentrations below cmc.Equilibrium adsorption isotherms of the surfactants on nylon particles were obtained from electrokinetic potentials of the particles dispersed in aqueous surfactant solutions at different temperatures. The equilibrium constants of adsorption, K, and the saturated adsorption amount, Ts, were determined from langmuir plots. The values of K and Ts obtained … More by the electro-kinetic method were compared with those by the electiric conductivity method. The values of K by the both agreed with each other. The difference in values of Ts provided information on the slipping plane and the dissociation degree of adsorbed surfactants.Adsorption rate constants were estimated from the desorption rate and equilibrium constants assuming the second-order kinetics. The desorption rate constants were determined in the range of 1 - 6 sec^<-1> and the adsorption rate constants to be in 2 - 8 x 10^4 mol^<-1>dm^3sec^<-1>, the former decreased and the latter increased with increasing number of carbon atoms in akkyl chain of the surfactants.The temperature dependence of desorption rate in the early stage of the process was investigated by an electric conductivity stopped-flow system newly developed. Activation energy of desorption was calculated to be 65.5 kJ/mol form Arrhenius plot, which was almost equal to the enthalpy of adsorption estimated in the same system. Less