表面活性剂AOT在聚乙二醇200和水混合溶液中聚集行为的研究

Aggregation Behavior of Sodium Bis (2-ethylhexyl) Sulfosuccinate in Polyethylene Glycol 200 and Water Mixed Solvent Media

采用表面张力、稳态荧光、电导率、微量热(ITC)等方法研究了表面活性剂磺酸钠琥珀酸二辛酯(AOT)在不同质量分数的聚乙二醇200(PEG 200)与水混合溶液中的聚集行为.研究表明,随着混合溶剂中PEG 200质量分数的增加,体系临界胶束浓度(cmc)有了显著的提高且胶束结构更加松散,推测与混合溶剂极性降低、烷基链和PEG 200之间的疏溶剂作用降低以及“结构破坏效应”有关.一般情况下,cmc是胶束形成难易程度的度量,因此认为PEG 200的加入不利于胶束的形成.通过质量作用模型计算胶束形成过程中的热力学函数发现,与纯水相比,混合体系中PEG 200含量较低(<60 wt%)时,低聚物的加入降低了体系中胶束的反离子解离度,从而使得体系吉布斯自由能△Gm^o变的更负;当PEG 200在溶剂中含量较高时,体系吉布斯自由能△Gm^o变的更正.由热力学参数(△Hm^o和-T△Sm^o)的数值可知,对于纯水体系或体系中PEG 200含量较高(≥80 wt%)时,胶束形成是熵驱动过程,其它体系是熵焓共驱过程.

Micellization behavior of sodium bis(2-ethylhexyl)sulfosuccinate(AOT)in mixed solvent media of polyethylene glycol 200(PEG 200)and water with varying mass fractions of PEG 200 has been studied by surface tension,steady-state fluorescence,electrical conductivity and Isothermal titration calorimetry(ITC)methods.The results showed that the critical micelle concentration(cmc)of AOT increased and the micelle structure is more loose with increasing PEG 200 amount in mixed solvent,it is speculated that the weak polarity of mixed solvent,the decreased solvophobic interaction between the alkyl chain and PEG 200,and“structure-breaking effect”might explain the experimental phenomena.In general,cmc is used as a measure of the ease of formation of micelles,so the addition of PEG 200 was not conducive to the formation of micelles.However,if the thermodynamic function in the micelle formation process was calculated by the mass action model,compared with pure water,it was found that when the content of PEG 200 in the mixed solvent was lower(<60 wt%),the addition of oligomers reduced the degree of counterion dissociation of the micelles in the system,making the system standard Gibbs free energy(△Gm^o)became more negative.When the content of PEG 200 in the mixed solvent was higher,the system Gibbs free energy became more positive.The values of the other two thermodynamic parameters(△Hm^o and-T △Sm^o)indicated that the micelle formation was entirely entropy driven for the systems with pure water or high content of PEG 200(≥80 wt%).The other systems were driven by entropic as well as enthalpic contributions.