Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Furo-cho B2-3(611), Chikusa, Nagoya, Aichi 464-8603, Japan.
J Chem Phys. 2010 Mar 21;132(11):114502. doi: 10.1063/1.3354117.
The mode-coupling theory for molecular liquids based on the interaction-site model is applied to a representative molecular ionic liquid, dimethylimidazolium chloride, and dynamic properties such as shear viscosity, self-diffusion coefficients, reorientational relaxation time, electric conductivity, and dielectric relaxation spectrum are analyzed. Molecular dynamics (MD) simulation is also performed on the same system for comparison. The theory captures the characteristics of the dynamics of the ionic liquid qualitatively, although theoretical relaxation times are several times larger than those from the MD simulation. Large relaxations are found in the 100 MHz region in the dispersion of the shear viscosity and the dielectric relaxation, in harmony with various experiments. The relaxations of the self-diffusion coefficients are also found in the same frequency region. The dielectric relaxation spectrum is divided into the contributions of the translational and reorientational modes, and it is demonstrated that the relaxation in the 100 MHz region mainly stems from the translational modes. The zero-frequency electric conductivity is close to the value predicted by the Nernst-Einstein equation in both MD simulation and theoretical calculation. However, the frequency dependence of the electric conductivity is different from those of self-diffusion coefficients in that the former is smaller than the latter in the gigahertz-terahertz region, which is compensated by the smaller dispersion of the former in the 100 MHz region. The analysis of the theoretical calculation shows that the difference in their frequency dependence is due to the different contribution of the short- and long-range liquid structures.
基于相互作用位点模型的分子液体的模式耦合理论被应用于一种有代表性的分子离子液体，即二甲基咪唑氯，并分析了其剪切黏度、自扩散系数、重取向弛豫时间、电导率和介电弛豫谱等动态特性。还对同一体系进行了分子动力学（MD）模拟以进行比较。尽管理论弛豫时间是 MD 模拟的数倍，但该理论定性地捕捉到了离子液体动力学的特征。在剪切黏度和介电弛豫的色散中，在 100 MHz 区域发现了较大的弛豫，这与各种实验结果一致。自扩散系数的弛豫也出现在相同的频率区域。介电弛豫谱被分为平移和重取向模式的贡献，证明在 100 MHz 区域的弛豫主要来自平移模式。零频电导率在 MD 模拟和理论计算中都接近 Nernst-Einstein 方程预测的值。然而，电导率的频率依赖性与自扩散系数不同，因为在前一个区域中，在千兆赫至太赫兹区域，电导率比自扩散系数小，这在前一个区域的 100 MHz 区域的较小色散中得到了补偿。理论计算的分析表明，它们在频率依赖性上的差异是由于短程和长程液体结构的不同贡献所致。
