含酯基Gemini表面活性剂在有机醇-水体系中的胶束热力学及聚集行为

摘要

采用电导法研究了不同温度下含酯基Gemini表面活性剂在纯水和在质量分数为10％的甲醇-水(MA-WR),乙二醇-水(EG-WR),丙三醇-水(GL-WR)四种体系中的集聚行为和胶束热力学;聚集行为参数包括临界胶束浓度(cmc)和抗衡离子的解离程度(α)以及胶束的热力学参数,包括标准吉布斯自由能(△G°m)、吉布斯迁移自由能(△G°trans)、吉布斯烷基链胶束化自由能(△G°tail)、标准焓变(△H°m)和标准熵变(△S°m),均被计算和讨论.研究表明在所有的研究体系中,cmc值随着疏水链的增加而减小,随着加入的醇结构中羟基数目的增加而增大,随温度的升高先变小,后变大呈U字形;胶束化过程都是自发进行的,并且在293.15 K下,胶束化过程是吸热的,在293.15 K上,胶束化过程是放热的;通过稳态荧光光谱法研究了表面活性剂在纯水、有机醇-水混合溶液中的微极性,结果表明,在相同溶剂中,随着烷基链长度的增加,溶液微环境的疏水性越强;对于相同的Gemini表面活性剂,随着加入含羟基数目越多的醇,其微环境的疏水性越强.并研究了Gemini表面活性剂在混合体系中形成胶束过程的焓-熵补偿曲线.%The aggregation behavior and thermodynamics of micellization for three Gemini surfactants with diester and rigid spacers in pure water and 10％ (mass fraction) organic alcohol-water co-solvents (MA-WR,EG-WR and GL-WR) across a range of temperatures from 283.15 to 308.15 K were investigated by electrical conductivity measurements.The aggregation behavior parameters,including critical micelle concentration (cmc),degree of counter ion dissociation (α),and the thermodynamic parameters of micellization including standardGibbs energy (△G°m),Gibbs energy of transfer (△G°trans),Gibbs energy of micellization per alkyl tail (△G°tail),standard enthalpy (△H°m),and standard entropy (△S°m) were calculated and discussed.Gemini surfactants with longer hydrophobic chain length have a lower cmc value,which was found to increase with the increasing number of hydroxyl groups of the alcohol in the organic mixed solvent.The temperature dependence of the cmc value for the Gemini surfactants was U-shaped in all the investigated systems.The micellization process is spontaneous,is endothermic at temperatures below 293.15 K,and becomes exothermic at temperatures above 293.15 K.The micropolarity of the Gemini surfactants in pure water and organic alcohol-water co-solvents were evaluated by steady-state fluorescence spectroscopy.The results showed that the hydrophobicity of the microenvironment for Gemini surfactant solutions becomes stronger with the increasing chain length of the surfactants and the number of hydroxyl groups of the alcohol in the organic mixed solvents.The compensation between the enthalpy and entropy for micellization of all the three gemini surfactants were observed in all the studied mixed media.