Tuning the dynamics of imidazolium-based ionic liquids via hydrogen bonding. I. The viscous regime.
Tuning the dynamics of imidazolium-based ionic liquids via hydrogen bonding. I. The viscous regime.
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DOI：
10.1063/5.0026144
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发表时间：
2020-11
期刊：
影响因子：
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通讯作者：
C. Thomann;P. Münzner;K. Moch;J. Jacquemin;P. Goodrich;A. Sokolov;R. Böhmer;C. Gainaru
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文献类型：
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作者：
C. Thomann;P. Münzner;K. Moch;J. Jacquemin;P. Goodrich;A. Sokolov;R. Böhmer;C. Gainaru
结合阻抗谱和振荡剪切流变学的结果，目前的工作重点是质量流和电荷流之间的关系，以及它们如何受到粘性离子液体 (IL) 中氢键的影响。特别是，我们比较了示例性IL 1-乙基-3-甲基咪唑鎓双(三氟甲基磺酰基)亚胺(EMIM-TFSI)及其OH官能化对应物1-(2-羟乙基)-3-甲基咪唑鎓双(三氟甲基磺酰基)亚胺(OHEMIM-TFSI)的弛豫行为。我们的结果和分析表明，阳离子 OH 基团的存在对 OHEMIM-TFSI 的整体动力学产生强烈影响，尽管在介电和机械响应中无法识别超结构弛豫模式的特征。为了检查这种强烈变化的根源是氢键还是仅仅是相应阳离子尺寸之间的差异（控制流体力学体积和电荷间距离），本研究包括1-丙基-3-甲基咪唑鎓双（三氟甲基磺酰基）亚胺（PMIM-TFSI）、EMIM-TFSI和PMIM-TFSI与双（三氟甲基磺酰基）亚胺锂（Li-TFSI）的混合物，以及OHEMIM-TFSI 与 PMIM-TFSI 的混合物。他们的研究清楚地表明，氢键引起的动力学变化明显大于离子尺寸变化引起的动力学变化。此外，在 OHEMIM-TFSI 与 PMIM-TFSI 的混合物中，OH 基团的稀释导致与理想混合行为的强烈偏差，从而突出了羟基功能化 IL 和其他氢键液体的共同现象学基础。
Combining results from impedance spectroscopy and oscillatory shear rheology, the present work focuses on the relation between the mass and charge flows and on how these are affected by the H-bonding in viscous ionic liquids (ILs). In particular, we compare the relaxational behaviors of the paradigmatic IL 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) and its OH-functionalized counterpart 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (OHEMIM-TFSI). Our results and their analysis demonstrate that the presence of cationic OH-groups bears a strong impact on the overall dynamics of OHEMIM-TFSI, although no signatures of suprastructural relaxation modes could be identified in their dielectric and mechanical responses. To check whether at the origin of this strong variation is the H-bonding or merely the difference between the corresponding cation sizes (controlling both the hydrodynamic volume and the inter-charge distance), the present study includes 1-propyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (PMIM-TFSI), mixtures of EMIM-TFSI and PMIM-TFSI with lithium bis(trifluoromethylsulfonyl)imide (Li-TFSI), and mixtures of OHEMIM-TFSI with PMIM-TFSI. Their investigation clearly reveals that the dynamical changes induced by H-bonding are significantly larger than those that can be attributed to the change in the ion size. Moreover, in the mixtures of OHEMIM-TFSI with PMIM-TFSI, a dilution of the OH-groups leads to strong deviations from ideal mixing behavior, thus highlighting the common phenomenological ground of hydroxy-functionalized ILs and other H-bonded liquids.