Alkoxy chain effect on the viscosity of a quaternary ammonium ionic liquid: molecular dynamics simulations.
Alkoxy chain effect on the viscosity of a quaternary ammonium ionic liquid: molecular dynamics simulations.
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DOI：
10.1021/jp807833a
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发表时间：
2009-01
期刊：
影响因子：
--
通讯作者：
L. Siqueira;M. Ribeiro
中科院分区：
文献类型：
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作者：
L. Siqueira;M. Ribeiro
当其中一条烷基链被烷氧链取代时，以季铵盐阳离子为基础的离子液体的粘度降低（Zhou等）。化学。欧元。[j] . 2005,11, 752.]． 通过分子动力学（MD）模拟，给出了醚函数在降低季铵离子液体粘度中所起作用的微观图像。对离子液体n -乙基- n， n -二甲基- n -（2-甲氧基乙基）二（三氟甲烷磺酰）亚胺（MOENM(2)E TFSI）的模型与四烷基铵的对应物进行了比较。在相同密度和温度下，烷氧基衍生物比四烷基体系具有更低的粘度、更高的离子扩散系数和更高的电导率。在阳离子-阳离子关系中观察到醚函数对液体结构的明显影响，而在阴离子-阴离子或阴离子-阳离子关系中则没有。在烷基和烷氧离子液体中，在胶束状结构中存在相邻阳离子的长链聚集。MD模拟表明，与烷基链相比，更灵活的烷氧基链之间的组装效率较低，这是MOENM(2)E TFSI中离子迁移率较高的结构原因。
The viscosity of ionic liquids based on quaternary ammonium cations is reduced when one of the alkyl chains is replaced by an alkoxy chain ( Zhou et al. Chem. Eur. J. 2005 , 11 , 752. ). A microscopic picture of the role played by the ether function in decreasing the viscosity of quaternary ammonium ionic liquids is provided here by molecular dynamics (MD) simulations. A model for the ionic liquid N-ethyl-N,N-dimethyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide, MOENM(2)E TFSI, is compared to the tetraalkylammonium counterpart. The alkoxy derivative has lower viscosity, higher ionic diffusion coefficients, and higher conductivity than the tetraalkyl system at the same density and temperature. A clear signature of the ether function on the liquid structure is observed in cation-cation correlations, but not in anion-anion or anion-cation correlations. In both the alkyl and the alkoxy ionic liquids, there is aggregation of long chains of neighboring cations within micelle-like structures. The MD simulations indicate that the less effective assembly between the more flexible alkoxy chains, in comparison to alkyl chains, is the structural reason for higher ionic mobility in MOENM(2)E TFSI.