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Isotropic ordering of ions in ionic liquids on the sub-nanometer scale†
Chemical Science ( IF 7.6 ) Pub Date : 2017-12-22 00:00:00 , DOI: 10.1039/c7sc05184k
Hailong Chen 1, 2, 3, 4, 5 , Xin Chen 6, 7, 8, 9, 10 , Jingwen Deng 6, 7, 8, 9, 10 , Junrong Zheng 6, 7, 8, 9, 10
Affiliation  

This article investigates structures of ionic liquids. Using a high-powered multiple-mode two dimensional infrared spectroscopic technique, we measure the anisotropy of interionic vibrational coupling in ionic liquids. Such anisotropy reports the relative orientation between cations and anions. Surprisingly, opposite to the well-propagated idea of ion pairing, a random orientation between the nearest non-spherically symmetric cation and anion is observed in ionic liquids. On the one hand, numerous previous experiments and theoretical calculations have shown that ionic liquids are highly ordered at the mesoscale, forming a bicontinuous nanostructure of ionic domains and hydrophobic domains. On the other hand, our results clearly prove that the ion ordering within the ionic domains is essentially random. Such an ordering at the larger scale (nanometers) and a lack of ordering at the smaller scale (sub-nanometer) is very rare for most liquids, or may even be unique to ionic liquids. Herein, we propose that ionic liquids may be regarded as 3D interconnecting nanocomposites of molten-salt-like domains and molecular-liquid-like domains. Such unique structuring could explain the fact that ionic liquids, like composite materials, often possess favorable properties of both “ionic” and “molecular” components.

中文翻译:

亚纳米尺度上离子液体中离子的各向同性排序

本文研究了离子液体的结构。使用高功率多模二维红外光谱技术,我们测量了离子液体中离子振动耦合的各向异性。这种各向异性报告了阳离子和阴离子之间的相对取向。出人意料的是,与广为传播的离子对概念相反,在离子液体中观察到了最接近的非球形对称阳离子和阴离子之间的随机取向。一方面,许多先前的实验和理论计算表明,离子液体在中尺度高度有序,形成了离子域和疏水域的双连续纳米结构。另一方面,我们的结果清楚地证明,离子域内的离子顺序基本上是随机的。对于大多数液体来说,这种较大规模(纳米)的有序性和较小规模(亚纳米)的无序性是非常罕见的,甚至可能是离子液体所独有的。在本文中,我们建议将离子液体视为熔融盐状结构域和分子液状结构域的3D互连纳米复合材料。这种独特的结构可以解释这样一个事实,即离子液体像复合材料一样,通常同时具有“离子”和“分子”成分的良好特性。
更新日期:2017-12-22
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