Department of Physical Chemistry, Faculty of Chemistry, University of Mazandaran, Babolsar, Iran.
J Phys Chem B. 2012 Sep 20;116(37):11517-26. doi: 10.1021/jp3059933. Epub 2012 Sep 5.
Structures and dynamics of nine geminal dicationic ionic liquids (DILs) Cn(mim)2X2, where n = 3, 6, and 9 and X = PF6(-), BF4(-), and Br(-), were studied by molecular dynamic simulations (J. Phys. Chem.B2004, 108, 2038-2047). A force field with a minor modification for C3(mim)2 × 2 was adopted for the simulations. Densities, detailed microscopic structures, mean-square displacements (MSD), and self-diffusivities for various ion pairs from MD simulations have been presented. The calculated densities for C9(mim)2X2 (X = Br(-) and BF4(-)) agreed well with the experimental values. The calculated RDFs show that anions are well organized around the imidazolium rings. The calculated RDFs indicate that, unlike the mono cationic ILs, the anions and cations in DILs distribute homogeneously. Enthalpies of vaporization were calculated and correlated with the structural features of DILs. The local structure of C9(mim)2X2 (X = Br, PF6) was examined by the spatial distribution function (SDF). The calculated SDFs show that similar trends were found by other groups for mono cationic ionic liquids (ILs). The highest probability densities are located around the imidazolium ring hydrogens. The calculated diffusion coefficients show that the ion diffusivities are 1 order of magnitude smaller than that of the mono cationic ionic liquids. The effects of alkyl chain length and anion type on the diffusion coefficient were also studied. The dynamics of the imidazolium rings and the alkyl chain in different time scales have also discussed. The calculated transference numbers show that the anions have the major role in carrying the electric current in a DIL.
采用经过微小修正的 C3(mim)2 × 2 力场对 9 种偕二阳离子二价离子液体 (DIL) Cn(mim)2X2(n = 3、6 和 9，X = PF6(-)、BF4(-)和 Br(-)) 的结构和动力学进行了分子动力学模拟 (J. Phys. Chem. B 2004, 108, 2038-2047)。模拟中呈现了来自 MD 模拟的各种离子对的密度、详细微观结构、均方位移 (MSD) 和自扩散系数。对于 C9(mim)2X2(X = Br(-)和 BF4(-))，计算出的密度与实验值吻合较好。计算得到的 RDF 表明，阴离子在咪唑环周围排列良好。计算得到的 RDF 表明，与单阳离子 IL 不同，DIL 中的阴离子和阳离子均匀分布。计算了蒸发焓，并将其与 DIL 的结构特征相关联。通过空间分布函数 (SDF) 研究了 C9(mim)2X2(X = Br、PF6)的局部结构。计算出的 SDF 表明，其他小组对单阳离子离子液体 (IL) 也发现了类似的趋势。最高概率密度位于咪唑环氢原子周围。计算出的扩散系数表明，离子扩散系数比单阳离子离子液体小一个数量级。还研究了烷基链长度和阴离子类型对扩散系数的影响。还讨论了不同时间尺度下的咪唑环和烷基链动力学。计算出的迁移数表明，在 DIL 中，阴离子在载流中起着主要作用。
