The heterogeneity in dynamics has important consequences for understanding the viscosity, diffusion, ionic mobility, and the rates of chemical reactions in technology relevant systems such as polymers, metallic glasses, aqueous solutions, and inorganic materials. Herein, we study the spatial and dynamic heterogeneities in ionic liquids by means of solid state NMR spectroscopy. In the ²H spectra of the protic ionic liquid [TEA][OTf] we observe anisotropic and isotropic signals at the same time. The spectra measured below the melting temperature at 306 K could be simulated by a superposition of the solid and liquid line shapes, which provided the transition enthalpies between the rigid and mobile fractions. Consequently, we measured the spin–lattice relaxation times T₁ for the anisotropic and the isotropic signals for the temperature range between 203 and 436 K. Both dispersion curves could be fitted to models including rotational correlation times, activation barriers and rate constants. This approach allowed determining the rotational correlation times for the N–D molecular vector of the [TEA]⁺ cation in differently mobile environments. The mobility is only slightly different, as indicated by small differences in activation energies for these processes. The NMR correlation times for the highly mobile phase are linearly related to measured viscosities, which supports the applicability of the Stokes–Einstein–Debye relation.

中文翻译：

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氘核NMR揭示离子液体中的动态异质性†

动力学的异质性对于理解粘度，扩散，离子迁移率以及与技术相关的系统（例如聚合物，金属玻璃，水溶液和无机材料）中的化学反应速率具有重要意义。本文中，我们通过固态NMR光谱研究了离子液体中的空间和动态异质性。在质子离子液体[TEA] [OTf]的² H光谱中，我们同时观察到各向异性和各向同性信号。低于306 K的熔化温度下测得的光谱可以通过实线和液相线形状的叠加来模拟，这提供了刚性和移动级分之间的过渡焓。因此，我们测量了自旋-晶格弛豫时间T ₁对于203和436 K之间温度范围的各向异性和各向同性信号。两个色散曲线都可以拟合到模型，包括旋转相关时间，激活势垒和速率常数。这种方法可以确定在不同移动环境中[TEA] ⁺阳离子的N–D分子向量的旋转相关时间。迁移率仅略有不同，如这些过程中活化能的微小差异所表明。高流动相的NMR相关时间与测得的粘度呈线性关系，这支持了Stokes-Einstein-Debye关系的适用性。