Temperature-Dependent Surface Enrichment Effects in Binary Mixtures of Fluorinated and Non-Fluorinated Ionic Liquids
Temperature-Dependent Surface Enrichment Effects in Binary Mixtures of Fluorinated and Non-Fluorinated Ionic Liquids
复制标题
DOI：
10.1002/chem.201904438
复制
发表时间：
2020-01-07
影响因子：
4.3
通讯作者：
Steinrueck, Hans-Peter
中科院分区：
文献类型：
--
作者：
Heller, Bettina S. J.;Lexow, Matthias;Steinrueck, Hans-Peter
利用角度分辨X射线光电子能谱(ARXPS)研究了不同二元离子液体(IL)混合物在不同温度下的液态顶端纳米结构。混合物由具有相同[Pf6](-)阴离子但具有两种不同阳离子的ILS组成，即3-methyl-1-(3，3，4，4，4-pentafluorobutyl)imidazolium六氟磷酸盐[PFBMIm][Pf6]和1-丁基-3-甲基咪唑六氟磷酸盐[C(4)C(1)Im][Pf6]，[PFBMIm][Pf6]的摩尔分数分别为10、25、50和75%。我们观察到，相对于本体组成，最上层的氟化链优先浓缩，这在[PFBMIm][PF6]含量最低的情况下最为明显。当混合物从95℃开始逐步冷却，直到XPS中的表面电荷效应表明固化时，我们观察到随着液态温度的降低，氟化链的表面浓缩显著增加。与[PFBMIm][PF6]含量较低的混合物相比，冷却75mol%的混合物在完全凝固前氟化链信号急剧下降，这归因于部分析出效应。
Using angle-resolved X-ray photoelectron spectroscopy (ARXPS), we investigate the topmost nanometers of various binary ionic liquid (IL) mixtures at different temperatures in the liquid state. The mixtures consist of ILs with the same [PF6](-) anion but two different cations, namely 3-methyl-1-(3,3,4,4,4-pentafluorobutyl)imidazolium hexafluorophosphate, [PFBMIm][PF6], and 1-butyl-3-methylimidazolium hexafluorophosphate, [C(4)C(1)Im][PF6], with 10, 25, 50 and 75 mol % content of [PFBMIm][PF6]. We observe a preferential enrichment of the fluorinated chain in the topmost layer, relative to the bulk composition, which is most pronounced for the lowest content of [PFBMIm][PF6]. Upon cooling the mixtures stepwise from 95 degrees C until surface charging effects in XPS indicate solidification, we observe a pronounced increase in surface enrichment of the fluorinated chain with decreasing temperature in the liquid state. In contrast to the mixtures with lower [PFBMIm][PF6] contents, cooling the 75 mol % mixture additionally shows an abrupt decrease of the fluorinated chain signal before complete solidification occurs, which is assigned to partial precipitation effects.