添加中低浓度离子液体[bmim][BF4]对吐温-20临界胶束浓度和胶束结构的影响

添加离子液体会对表面活性剂在水溶液中的聚集行为产生重要影响。本文研究了吐温-20在中低浓度离子液体四氟硼酸1-丁基-3-甲基咪唑鎓(bmim]BF_4])中的胶束化行为。随着bmim]BF_4]浓度(cIL)从0增加到0.2mol·L~(-1),吐温-20的临界胶束浓度逐渐增大。相比cIL0.05mol·L~(-1),在cIL0.05mol·L~(-1)时加入bmim]BF_4]使吐温-20临界胶束浓度增大得更加显著。吐温-20胶束聚集数随着离子液体浓度的增加而逐渐减小,这一结果也说明加入离子液体会对吐温-20胶束的生成有抑制作用。吐温-20胶束化热力学研究表明,吐温-20在不同浓度离子液体中的胶束化是熵、焓共同驱动,并具有熵-焓补偿性。随着离子液体浓度的增加,吐温-20胶束平均粒径和胶束微粘性均表现出先增大后减小的变化,在cIL=0.05mol·L~(-1)时达到最大值。

Influence of Medium-low Concentration of Ionic Liquid [bmim][BF4] on Critical Micellization Concentration and Micelle Structures

The presence of Ionic Liquids (ILs) has a significant impact on the aggregation behavior of surfactants in aqueous solution. In this article, micellization of non-ionic surfactant Tween-20 with the presence of middle and low concentration of hydrophilic ionic liquid bmim]BF4] (1-butyl-3-methylimidazolium tetrafluoroborate) was investigated. Critical Micellization Concentration (CMC) of Tween-20 showed an upward trend with increasing concentration of bmim]BF4] from 0 to 0.2 mol·L?1. When the concentration of IL exceeded 0.05 mol·L?1, bmim]BF4] showed more remarkable effects on increasing CMC of Tween-20, compared with IL concentration lower than 0.05 mol·L?1. Aggregation number of Tween-20 micelles decreased with increasing concentration of bmim]BF4], which also indicated that the presence of bmim]BF4] had great effect on hindering the micellization of Tween-20. Thermodynamic investigation of Tween-20 micellization demonstrated that the micellization of Tween-20 was driven by both entropy and enthalpy, and also showed entropy-enthalpy compensation. Meanwhile, average particle size and micro-viscosity of Tween-20 micelles increased first and then decreased with increasing concentration of bmim]BF4] from 0 to 0.2 mol·L?1, reaching peak values at CIL=0.05 mol·L?1. This result was attributed to the electrostatic and steric effects, hydrogen bond between ionic liquid and Tween-20 as well as the dramatically increased permeability of water molecules brought by the presence of bmim]BF4] associated to the palisade layer of Tween-20 and the diminished aggregation number.