Department of Chemistry, Faculty of Science, Fukuoka University, Jonan-ku, Fukuoka, Japan.
J Colloid Interface Sci. 2011 Apr 15;356(2):798-802. doi: 10.1016/j.jcis.2011.01.022. Epub 2011 Jan 12.
Micellization behavior was investigated for polyoxyethylene-type nonionic surfactants with varying chain length (C(n)E(m)) in a room temperature ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF(4)). Critical micelle concentration (cmc) was determined from the variation of (1)H NMR chemical shift with the surfactant concentration. The logarithmic value of cmc decreased linearly with the number of carbon atoms in the surfactant hydrocarbon chain, similarly to the case observed in aqueous surfactant solutions. However, the slope of the straight line is much smaller in bmimBF(4) than in aqueous solution. Thermodynamic parameters for micelle formation estimated from the temperature dependence of cmc showed that the micellization in bmimBF(4) is an entropy-driven process around room temperature. This behavior is also similar to the case in aqueous solution. However, the magnitude of the entropic contribution to the overall micellization free energy in bmimBF(4) is much smaller compared with that in aqueous solution. These results suggest that the micellization in bmimBF(4) proceeds through a mechanism similar to the hydrophobic interaction in aqueous surfactant solutions, although the solvophobic effect in bmimBF(4) is much weaker than the hydrophobic effect.
在室温离子液体 1-丁基-3-甲基咪唑四氟硼酸盐（bmimBF4）中，研究了具有不同链长（C(n)E(m)）的聚氧乙烯型非离子表面活性剂的胶束化行为。通过（1）H NMR 化学位移随表面活性剂浓度的变化来确定临界胶束浓度（cmc）。cmc 的对数与表面活性剂烃链中的碳原子数呈线性关系，这与在水相表面活性剂溶液中的情况相似。然而，在 bmimBF4 中的斜率比在水溶液中要小得多。从 cmc 的温度依赖性估算的胶束形成热力学参数表明，在 bmimBF4 中胶束化是一个在室温附近的熵驱动过程。这种行为也与在水溶液中的情况相似。然而，与在水溶液中相比，在 bmimBF4 中，熵对整个胶束化自由能的贡献要小得多。这些结果表明，尽管 bmimBF4 中的溶剂疏水性比疏水作用弱得多，但 bmimBF4 中的胶束化通过类似于水相表面活性剂溶液中的疏水相互作用的机制进行。
