Canongia Lopes José N A, Pádua Agílio A H
Centro de Química Estrutural, Instituto Superior Técnico, Lisboa, Portugal.
J Phys Chem B. 2006 Feb 23;110(7):3330-5. doi: 10.1021/jp056006y.
Nanometer-scale structuring in room-temperature ionic liquids is observed using molecular simulation. The ionic liquids studied belong to the 1-alkyl-3-methylimidazolium family with hexafluorophosphate or with bis(trifluoromethanesulfonyl)amide as the anions, [C(n)mim][PF(6)] or [C(n)mim][(CF(3)SO(2))(2)N], respectively. They were represented, for the first time in a simulation study focusing on long-range structures, by an all-atom force field of the AMBER/OPLS_AA family containing parameters developed specifically for these compounds. For ionic liquids with alkyl side chains longer than or equal to C(4), aggregation of the alkyl chains in nonpolar domains is observed. These domains permeate a tridimensional network of ionic channels formed by anions and by the imidazolium rings of the cations. The nanostructures can be visualized in a conspicuous way simply by color coding the two types of domains (in this work, we chose red = polar and green = nonpolar). As the length of the alkyl chain increases, the nonpolar domains become larger and more connected and cause swelling of the ionic network, in a manner analogous to systems exhibiting microphase separation. The consequences of these nanostructural features on the properties of the ionic liquids are analyzed.
利用分子模拟观察了室温离子液体中的纳米级结构。所研究的离子液体属于1-烷基-3-甲基咪唑鎓家族，分别以六氟磷酸根或双（三氟甲磺酰）酰胺为阴离子，即[C(n)mim][PF(6)]或[C(n)mim][(CF(3)SO(2))(2)N]。在一项专注于长程结构的模拟研究中，它们首次由AMBER/OPLS_AA家族的全原子力场表示，该力场包含专门为这些化合物开发的参数。对于烷基侧链长度大于或等于C(4)的离子液体，观察到烷基链在非极性区域聚集。这些区域贯穿由阴离子和阳离子的咪唑环形成的三维离子通道网络。只需通过对两种类型的区域进行颜色编码（在本工作中，我们选择红色 = 极性，绿色 = 非极性），就能以显著的方式可视化纳米结构。随着烷基链长度的增加，非极性区域变得更大且连接更紧密，并导致离子网络膨胀，其方式类似于表现出微相分离的体系。分析了这些纳米结构特征对离子液体性质的影响。
