Molecular dynamics simulation of nanostructural organization in ionic liquid/water mixtures
Molecular dynamics simulation of nanostructural organization in ionic liquid/water mixtures
复制标题
DOI：
10.1021/jp0671421
复制
发表时间：
2007-05-10
影响因子：
3.3
通讯作者：
Voth, Gregory A.
中科院分区：
文献类型：
--
作者：
Jiang, Wei;Wang, Yanting;Voth, Gregory A.
用分子动力学模拟方法研究了不同水浓度下1-辛基-3-甲基咪唑硝酸盐离子液体与水混合物中的纳米结构。通过偏径向分布函数对极性网络、水网络和胶束结构的演化进行了可视化和分析。计算的静态偏结构因子表明，在所考察的水分含量范围内，极性网络、水网络和胶束在20A左右具有近似不变的特征长度。此外，上述计算指出，随着水量的增加，极性网络不断被入侵的水破坏(屏蔽)，而水网络和胶束的结构结构呈现翻转。在转化点形成了最有序的胶束(阳离子-阳离子)结构和水(水-阴离子-水)网络。此后，结构组织急剧减弱，由于水-水相互作用占主导地位，只存在疏松的胶束结构。在类似离子液体的水溶液中，模拟的结构组织翻转与实验得到的结构因子中最尖锐的峰一致；模拟的水结构表明，由于NO3-的平面对称性和强碱性，水可以形成类液体缔合聚集体，这与实验结果一致。随着水含量的增加，胶束结构的转变是非极性基团的疏水相互作用持续竞争和带电网络破裂的结果，而水网络的转变是水-水和水-阴离子相互作用竞争的结果。
Molecular dynamics simulations have been carried out to investigate nanostructural organization in mixtures of 1-octyl-3-methylimidazolium nitrate ionic liquid and water at multiple water concentrations. Evolution of the polar network, water network, and micelle structures is visualized and analyzed via partial radial distribution functions. The calculated static partial structure factors show that within the range of water contents examined, polar networks, water networks, and micelles possess an approximately invariant characteristic length at around 20 A. Furthermore, the above calculations point out that, as the amount of water increases, the polar network is continuously broken up (screened) by the intruding water, while the structural organization of the water network and the micelle exhibits a turnover. At the turnover point, the most ordered micelle (cation-cation) structure and water (water-anion-water) network are formed. Thereafter, the structural organization abates drastically, and only loose micelle structure exists due to the dominant water-water interactions. The simulated turnover of structural organization agrees with the sharpest peak in the experimentally obtained structure factor in aqueous solutions of similar ionic liquids; the simulated water structure reveals that water can form liquidlike associated aggregates due to the planar symmetry and strong basicity of NO3-, in agreement with experiment. The turnover of structural organization of micelles results from the persistent competition between the hydrophobic interactions of the nonpolar groups and the breakup of the charged polar network with increasing water content, whereas the turnover of the water network results from the competition between the water-water and water-anion interactions.