Physicochemical properties and structures of room temperature ionic liquids. 2. Variation of alkyl chain length in imidazolium cation
Physicochemical properties and structures of room temperature ionic liquids. 2. Variation of alkyl chain length in imidazolium cation
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DOI：
10.1021/jp044626d
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发表时间：
2005-04-07
影响因子：
3.3
通讯作者：
Watanabe, M
中科院分区：
文献类型：
--
作者：
Tokuda, H;Hayamizu, K;Watanabe, M
通过改变1-烷基-3-甲基咪唑双（三氟甲烷磺酰基）亚胺([Rmim][(CF3-SO2)(2)N], R =甲基(m)，乙基(e)，丁基（b)，己基（C-6），辛基（C-8））的烷基链长，制备了一系列室温离子液体（RTILs），并在较宽温度范围内测量了阳离子和阴离子的热行为、密度、粘度、自扩散系数和离子电导率。自扩散系数、黏度、离子电导率和摩尔电导率随温度的变化遵循Vogel-Fulcher-Tamman方程，密度呈线性下降。脉冲场梯度自旋回波核磁共振方法显示，在较宽的温度范围内，即使阳离子半径大于阴离子半径，阳离子的自扩散系数也高于阴离子。RTILs的阳离子和阴离子扩散系数总和为[emim][(CF3SO2)(2)N] > [mmim][(CF3SO2)(2)N] > [bmim][(CF3SO2)(2)N] > [C(6)mim][(CF3SO2)(2)N] > [C(8)mim][(CF3SO2)(2)N]，与粘度数据有很大的对比。通过阻抗测量得到的摩尔电导率与使用能斯特-爱因斯坦方程通过离子扩散系数计算得到的摩尔电导率之比量化了扩散组分中有助于离子传导的活性离子，换句话说，就是离子液体的离子性。随着烷基链上碳原子数的增加，该比值减小。最后，讨论了静电和感应力之间的平衡，讨论了决定物理化学性质的主要因素。
The alkyl chain length of 1-alkyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide ([Rmim][(CF3-SO2)(2)N], R = methyl (m), ethyl (e), butyl (b), hexyl (C-6), and octyl (C-8)) was varied to prepare a series of room-temperature ionic liquids (RTILs), and the thermal behavior, density, viscosity, self-diffusion coefficients of the cation and anion, and ionic conductivity were measured over a wide temperature range. The self-diffusion coefficient, viscosity, ionic conductivity, and molar conductivity change with temperature following the Vogel-Fulcher-Tamman equation, and the density shows a linear decrease. The pulsed-field-gradient spin-echo NMR method reveals a higher self-diffusion coefficient for the cation compared to that for the anion over a wide temperature range, even if the cationic radius is larger than that of the anion. The summation of the cationic and anionic diffusion coefficients for the RTILs follows the order [emim][(CF3SO2)(2)N] > [mmim][(CF3SO2)(2)N] > [bmim][(CF3SO2)(2)N] > [C(6)mim][(CF3SO2)(2)N] > [C(8)mim][(CF3SO2)(2)N], which greatly contrasts to the viscosity data. The ratio of molar conductivity obtained from impedance measurements to that calculated by the ionic diffusivity using the Nernst-Einstein equation quantifies the active ions contributing to ionic conduction in the diffusion components, in other words, ionicity of the ionic liquids. The ratio decreases with increasing number of carbon atoms in the alkyl chain. Finally, a balance between the electrostatic and induction forces has been discussed in terms of the main contribution factor in determining the physicochemical properties.