自由能微扰法研究系列烷基芳基磺酸盐的胶束化焓-熵补偿现象

为了研究不同结构的表面活性剂分子在水溶液中的胶束化焓-熵补偿现象, 采用自由能微扰(FEP)法计算了系列烷基芳基磺酸盐的溶剂化自由能, 并根据胶团化过程的质量作用模型讨论了相关热力学性质. 结果表明: 自由能微扰法得到的溶剂化自由能大小与用传统热力学表面张力法测定的吉布斯自由能相近, 能够用于比较不同结构的烷基芳基磺酸盐间胶束化能力; 烷基芳基磺酸盐在水溶液中的胶束化过程是自发进行的, 且存在焓-熵补偿现象, 补偿温度范围均在(302±2) K; 随着分子结构中芳环向长烷基链中间位置移动, 胶束化能力和胶束的稳定性均下降; 而随着芳环上短烷基链或长烷基链碳数的增加, 形成胶束的能力与稳定性均提高.

Free Energy Perturbation of Enthalpy-Entropy Compensation for the Micellization of Alkyl Aryl Sulfonates

We used the free energy perturbation(FEP) method to calculate the solvation free energy according to the mass action model.We did this to investigate the enthalpy-entropy compensation effect of surfactant molecular structures on micellization in solution.The thermodynamic properties of micellization in an aqueous solution for several alkyl aryl sulfonates are discussed.Results show that the solvation free energy calculated from the free energy perturbation is consistent with that from the surface tension method and can be used to discriminate between the capacities of micellization for alkyl aryl sulfonates.The micellization of alkyl aryl sulfonate in an aqueous solution is a spontaneous process and the micellization is enthalpy-entropy compensated.The compensation temperature was found to be(302±2) K.As the aromatic ring shifts from the edge to the middle of the long carbon chain,the formation ability of the micelle and micelle stability decrease.However,with an increase in the number of carbon atoms on the short or long alkyl chains on the aromatic rings the formation ability and the stability of the micelles increase.