Ramya K R, Kumar Praveen, Kumar Ashish, Venkatnathan Arun
Department of Chemistry, Indian Institute of Science Education and Research , Pune 411008, India.
J Phys Chem B. 2014 Jul 24;118(29):8839-47. doi: 10.1021/jp504270b. Epub 2014 Jul 9.
A molecular investigation on the effect of water on structural properties of imidazolium-based ionic liquids (ILs) is essential due to its various industrial applications. In this work, we employ molecular dynamics simulations to characterize the influence of various water concentrations on nanostructural properties of the 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [Hmim][NTf2] IL. An examination of molecular interactions in [Hmim][NTf2] IL-water mixtures shows the following trends: (a) At low water concentration, small regions of water molecules are surrounded by several cation-anion pairs. (b) At medium water concentration, cation tail aggregation starts, and phase separation between the IL and water is observed. (c) At high water concentration, increasing cationic tail aggregation leads to micelle formation. Further aggregates of cations and anions are solvated by large water channels. The radial distribution functions show that cation-anion, cation-cation, and anion-anion interactions decrease and water-water interaction increases with water concentration. The hydrogen bonding interactions occur between the acidic hydrogen of the positively charged imidazolium cation with the nitrogen and oxygen atoms of the anions. However, no hydrogen bonding interactions are seen between water molecules and the hydrophobic anions.
由于咪唑基离子液体（ILs）具有多种工业应用，因此对水对其结构性质影响的分子研究至关重要。在这项工作中，我们采用分子动力学模拟来表征不同水浓度对1-己基-3-甲基咪唑双（三氟甲基磺酰）亚胺[Hmim][NTf2]离子液体纳米结构性质的影响。对[Hmim][NTf2]离子液体-水混合物中分子间相互作用的研究显示出以下趋势：（a）在低水浓度下，水分子的小区域被几个阳离子-阴离子对包围。（b）在中等水浓度下，阳离子尾部开始聚集，并观察到离子液体和水之间的相分离。（c）在高水浓度下，阳离子尾部聚集增加导致胶束形成。阳离子和阴离子的进一步聚集体被大的水通道溶剂化。径向分布函数表明，随着水浓度的增加，阳离子-阴离子、阳离子-阳离子和阴离子-阴离子相互作用减弱，而水-水相互作用增强。带正电的咪唑阳离子的酸性氢与阴离子的氮和氧原子之间发生氢键相互作用。然而，在水分子和疏水性阴离子之间未观察到氢键相互作用。
