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解吸动力学。采用铂电极对停流分光光度计混合池进行了改进，用于电导率检测。在解吸过程中，电导率随时间的变化由记忆记录系统监测。表面活性剂为烷基磺酸钠（C_<10>-C_<16>）。尼龙颗粒表面离子的解吸速率与表面活性剂的浓度无关，在浓度低于cmc的情况下，应用一级反应方案得到了解吸速率常数。通过不同温度下分散在表面活性剂水溶液中的颗粒的电动势，得到了表面活性剂在尼龙颗粒上的平衡吸附等温线。用langmuir图测定了吸附平衡常数K和饱和吸附量Ts。并将电动力学法测得的K和Ts值与电导率法测得的进行了比较。两者的K值是一致的。Ts值的差异提供了滑动面和吸附表面活性剂解离程度的信息。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。解吸速率常数在1 ~ 6 mol^<-1>范围内，吸附速率常数在2 ~ 8 × 10^4 mol^<-1>dm^3sec^<-1>范围内，前者随表面活性剂烷基链碳原子数的增加而减小，后者随碳原子数的增加而增大。采用新研制的电导率停止流系统，研究了解吸过程早期温度对解吸速率的依赖性。由阿伦尼乌斯图计算得到的脱附活化能为65.5 kJ/mol，与同一体系的吸附焓基本相等。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