In this investigation, we examine the effect of water concentration and temperature on the dynamical properties of [Hmim][Cl] and [Hmim][NTf₂] ionic liquids (ILs). The dynamical properties such as translational diffusion coefficients, ion-pair lifetimes, and rotational correlation times are calculated using molecular dynamics simulations. The simulations predict that water concentration also significantly impacts the magnitude of dynamical properties. At low, intermediate and high water concentrations, the following trend in diffusion coefficients is seen: Cl⁻ > Hmim⁺; Cl⁻ > NTf₂⁻; Hmim⁺ ([Hmim][Cl]) > Hmim⁺ ([Hmim] [NTf₂]). At ultra-low water concentrations of [Hmim][Cl] IL, several bridge like configurations form between water molecules and Cl⁻ anions, which are supported by a complex distribution of water clusters. The effect of an increase in the water concentration leads to a decrease in ion-pair lifetimes between the Hmim⁺ cations and Cl⁻/NTf₂⁻ anions, which strongly correlates with the trends observed from the diffusion coefficients. A biexponential function was found to be the best fit for the RACF at neat/ultra-low water concentrations of [Hmim][Cl] and [Hmim][NTf₂] ILs, whereas a single exponential function was sufficient to fit the RACF at low, intermediate and high water concentrations. The rotational relaxation time of the Hmim⁺ cations is larger in neat [Hmim][Cl] compared to that in neat [Hmim][NTf₂] with an opposite trend seen with hydration. The rotational correlation time of water molecules is larger in [Hmim][Cl] compared to that in [Hmim][NTf₂] at low and intermediate water concentrations, with similar correlation times observed at high water concentrations.

中文翻译：

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探索基于亲水/疏水阴离子的咪唑鎓离子液体-水混合物的平移和旋转动力学†

在这项研究中，我们研究了水浓度和温度对[Hmim] [Cl]和[Hmim] [NTf ₂ ]离子液体（ILs）动力学性质的影响。使用分子动力学模拟计算动力学特性，例如平移扩散系数，离子对寿命和旋转相关时间。模拟预测，水的浓度还会显着影响动力学特性的大小。在低，中，高的水浓度，在扩散系数以下趋势看出值：Cl ^- > HMIM ⁺ ; 氯^- > NTF ₂ ^- ; Hmim ⁺（[Hmim] [Cl]）> Hmim ⁺（[Hmim] [NTf ₂]）。在[HMIM] [CL] IL的超低水浓度，多个桥状结构的水分子和Cl之间形成^-的阴离子，其通过水簇的一个复杂的分布支撑。增加的水浓度引线在HMIM之间离子对寿命的降低的效果⁺阳离子和Cl ^- / NTF ₂ ^-的阴离子，其强烈地与来自扩散系数观察到的趋势相关。发现在[Hmim] [Cl]和[Hmim] [NTf ₂ ]的净水/超低水浓度下，双指数函数最适合RACFILs，而单个指数函数足以在低，中和高水浓度下拟合RACF。与纯净的[Hmim] [NTf ₂ ]相比，纯净的[Hmim] [Cl]中Hmim ⁺阳离子的旋转弛豫时间更长，而水合则呈现相反的趋势。在低和中等水浓度下，[Hmim] [Cl]中水分子的旋转相关时间比[Hmim] [NTf ₂ ]中大，在高水浓度下观察到相似的相关时间。