The University of Melbourne, Melbourne, VIC 3031, Australia.
J Phys Chem B. 2010 Sep 9;114(35):11436-43. doi: 10.1021/jp105087n.
NMR relaxation and diffusion characterization of several protic ionic liquids at high and low magnetic fields are reported. The dynamics of cations and anions were similar at both frequencies, with similar trends and magnitudes for a fixed component paired with oppositely charged species. An Arrhenius relationship was displayed between the molecular motion and the glass transition temperature. The diffusion of ions showed a strong degree of ion correlation between cation and anion, and Arrhenius plots of relaxation and diffusion indicated that the ions diffused as a pair. At high field diffusion was dominated by mobile species that followed Stokes-Einstein behavior. Conversely, diffusion observed at low field emphasized relatively immobile species that displayed fractional Stokes-Einstein behavior. No evidence was found to indicate the influence of magnetic field on structural and dynamic properties of the studied ILs; however, variation between diffusion coefficients at different magnetic fields indicated dynamic heterogeneities (or temporal aggregates) within the ionic liquid.
报道了几种质子离子液体在高磁场和低磁场下的 NMR 弛豫和扩散特性。在这两种频率下，阳离子和阴离子的动力学相似，对于固定组分与带相反电荷的物质对，具有相似的趋势和幅度。分子运动与玻璃化转变温度之间呈现出阿仑尼乌斯关系。离子的扩散表现出阳离子和阴离子之间强烈的离子相关性，弛豫和扩散的阿仑尼乌斯图表明离子以对的形式扩散。在高磁场中，扩散主要由遵循斯托克斯-爱因斯坦行为的可移动物质控制。相反，在低场观察到的扩散强调了表现出分数斯托克斯-爱因斯坦行为的相对不可移动的物质。没有证据表明磁场会影响所研究 ILs 的结构和动力学性质；然而，不同磁场下扩散系数的变化表明离子液体内部存在动态不均匀性（或暂时聚集体）。
