Aggregation behavior of polyoxyethylene (20) sorbitan monolaurate (tween 20) in imidazolium based ionic liquids.
Aggregation behavior of polyoxyethylene (20) sorbitan monolaurate (tween 20) in imidazolium based ionic liquids.
复制标题
DOI：
10.1021/la801358z
复制
发表时间：
2008-07
期刊：
影响因子：
--
通讯作者：
Jiapei Wu;Na Li;Liqiang Zheng;Xinwei Li;Yanan Gao;Tohru Inoue
中科院分区：
文献类型：
--
作者：
Jiapei Wu;Na Li;Liqiang Zheng;Xinwei Li;Yanan Gao;Tohru Inoue
测定了聚氧乙烯（20）失水山梨醇单月桂酸酯（Tween 20）在1-丁基-3-甲基咪唑四氟硼酸盐（bmimBF 4）和六氟磷酸盐（bmimPF 6）中的表面张力。在每个温度下的表面张力-浓度曲线上发现了两个转变点。冷冻断裂透射电子显微镜显示，两种不同尺寸的颗粒形成在每个过渡点的浓度。因此，两个转变点的表面活性剂浓度被视为临界聚集浓度，CAC 1和CAC 2。从CAC值和它们的温度依赖性，我们估计了聚集体形成的热力学参数，Δ G agg（0），Δ H agg（0）和Δ S agg（0）。与CAC 1有关的热力学参数几乎与温度无关。另一方面，对于CAC 2处的聚集体形成，在低温下，正的Δ S agg（0）有助于负的Δ G agg（0），而在高温下，负的Δ H agg（0）有助于负的Δ G agg（0）。热力学参数作为温度的函数的行为，结合作为表面活性剂浓度的函数的bmim（+）质子的（1）H NMR化学位移的变化，表明在CAC 1形成的聚集体是从溶液相分离的吐温20的纳米液滴，而在CAC 2形成的聚集体类似于在水溶液中形成的通常的表面活性剂胶束。
Surface tension measurements were carried out for the solutions of polyoxyethylene (20) sorbitan monolaurate (Tween 20) in 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF 4) and hexafluorophosphate (bmimPF 6) at various temperatures. Two transition points were found in the surface tension-concentration curves at each temperature. The freeze-fracture transmission electron microscopy revealed that two kinds of particles with different sizes are formed at the concentrations of each transition point. Thus, the surfactant concentrations of the two transition points are regarded as critical aggregation concentrations, CAC 1 and CAC 2. From the CAC values and their temperature dependence, we estimated the thermodynamic parameters of the aggregate formation, Delta G agg (0), Delta H agg (0), and Delta S agg (0). The thermodynamic parameters related to CAC 1 are almost independent of temperature. On the other hand, as for the aggregate formation at CAC 2, a positiveDelta S agg (0) contributes to a negative Delta G agg (0) at low temperature, while a negative Delta H agg (0) contributes to a negative Delta G agg (0) at high temperature. The behavior of the thermodynamic parameters as a function of temperature, combined with the variation of (1)H NMR chemical shifts of the bmim (+) protons as a function of the surfactant concentration, demonstrated that the aggregates formed at CAC 1 are nanodroplets of Tween 20 segregated from the solution phase, while those formed at CAC 2 are similar to the usual surfactant micelles formed in aqueous solution.