Division of Mathematics and Sciences, University of Tennessee Southern, Pulaski, TN, USA.
Department of Chemistry, US Naval Academy, Annapolis, MD, USA.
Phys Chem Chem Phys. 2023 Feb 22;25(8):6342-6351. doi: 10.1039/d2cp05863d.
Ion dynamics and charge transport in 1-methyl-3-octylimidazolium ionic liquids with chloride, bromide, tetrafluoroborate, tricyanomethanide, hexafluorophosphate, triflate, tetrachloroaluminate, bis(trifluoromethylsulfonyl)imide, and heptachlorodialuminate anions are investigated by broadband dielectric spectroscopy, rheology, viscometry, and differential scanning calorimetry. A detailed analysis reveals an anion and temperature-dependent separation of characteristic molecular relaxation rates extracted from various representations of the dielectric spectra. The separation in rates extracted from the electric modulus and conductivity formalisms is interpreted as an experimental signature of significant heterogeneity in the local ion dynamics associated with the structural glass transition, viscosity, and dc ion conductivity. It is further found that the degree of dynamic heterogeneity correlates with the strengths of slow dielectric and mechanical relaxations previously attributed to the dynamics of mesoscale solvophobic aggregates. Increasing local dynamic heterogeneity correlates with an increase in the strength of the slow, aggregate dielectric relaxation and a decrease in the strength of the slow, aggregate mechanical relaxation. Accordingly, increasing local dynamic heterogeneity, brought about by change in temperature and/or cation/anion chemical structure, correlates with an increase in the static dielectric permittivities and a decrease in the contribution of aggregate dynamics to the zero-shear viscosities. The established correlation provides a new ability to distinguish between the influence of mesoscale aggregate shape/morphology local and mesoscale ion dynamics on the transport properties of ionic liquids.
通过宽带介电谱、流变学、粘度测量和差示扫描量热法研究了氯化物、溴化物、四氟硼酸盐、三氰胺、六氟磷酸盐、三氟甲磺酸酯、四氯铝酸盐、双（三氟甲基磺酰基）亚胺和七氯二铝酸盐阴离子在 1-甲基-3-辛基咪唑鎓离子液体中的离子动力学和电荷输运。详细分析揭示了从介电谱的各种表示中提取的特征分子弛豫率与阴离子和温度有关的分离。从电模量和电导率形式中提取的速率分离被解释为与结构玻璃化转变、粘度和直流离子电导率相关的局部离子动力学显著不均匀性的实验特征。进一步发现，动态异质性的程度与先前归因于介观疏水性聚集体动力学的慢介电和力学松弛的强度相关。局部动态异质性的增加与慢、聚集体介电松弛的强度增加以及慢、聚集体力学松弛的强度降低相关。因此，通过温度和/或阳离子/阴离子化学结构的变化引起的局部动态异质性的增加与静态介电常数的增加以及聚集体动力学对零剪切粘度的贡献的减少相关。所建立的相关性提供了一种新的能力，可以区分介观聚集体形状/形态和局部和介观离子动力学对离子液体输运性质的影响。
