Sugimori Yuki, Miyata Tomohiro, Hashiguchi Hiroki, Okunishi Eiji, Mizoguchi Teruyasu
Institute of Industrial Science, The University of Tokyo 4-6-1 Komaba Meguro Tokyo 153-8505 Japan
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University 2-1-1, Katahira, Aoba Sendai Miyagi 980-8577 Japan.
RSC Adv. 2019 Apr 4;9(19):10520-10527. doi: 10.1039/c8ra10386k. eCollection 2019 Apr 3.
Ionic liquids show characteristic properties derived from them being composed of only molecular ions, and have recently been used as solvents for chemical reactions and as electrolytes for electrochemical devices. The liquid structures, , ionic distributions, form when solutes are dissolved in ionic liquids and fundamentally affect the reactions and transfer efficiency in such solutions. In this study, we directly observe the liquid structure in a solution of the long-chain ionic liquid 1-octyl-3-methylimidazolium bromide (Cmim Br) and barium stearate (Ba(CHCOO)) using the annular dark-field method of scanning transmission electron microscopy (ADF-STEM). The ADF image shows a 10 nm-scale heterogeneity in the image intensity, which reflects the heterogeneous ionic distribution in the solution. The number density distributions of all the component ions (Cmim, Br, Ba, and CHCOO) were estimated from the ADF image intensity and then visualized. These ionic distribution maps depicted the spatial relationships between the ions at the sub-nanometer scale and revealed that the heterogeneity is largely derived from the large differences in size, charge distributions, and van der Waals interactions.
离子液体具有仅由分子离子组成所衍生出的特性，并且最近已被用作化学反应的溶剂和电化学装置的电解质。当溶质溶解在离子液体中时会形成液体结构、离子分布，这从根本上影响此类溶液中的反应和转移效率。在本研究中，我们使用扫描透射电子显微镜的环形暗场方法（ADF-STEM）直接观察长链离子液体1-辛基-3-甲基咪唑溴化物（Cmim Br）和硬脂酸钡（Ba(CHCOO)）溶液中的液体结构。ADF图像显示图像强度存在10纳米尺度的不均匀性，这反映了溶液中离子分布的不均匀性。根据ADF图像强度估算所有组分离子（Cmim、Br、Ba和CHCOO）的数密度分布，然后进行可视化。这些离子分布图描绘了亚纳米尺度下离子之间的空间关系，并揭示出这种不均匀性很大程度上源于尺寸、电荷分布和范德华相互作用的巨大差异。
