Department of Physical Chemistry II, Ruhr-University Bochum, D-44780 Bochum, Germany.
J Chem Phys. 2010 Sep 14;133(10):101101. doi: 10.1063/1.3478221.
We report on dielectric relaxation spectra of six homologous ionic liquids (ILs) with tetra(hexafluoroisopropoxy)aluminate (Al(hfip)(4)) as a common anion. The dominating mode on the time scale of several 100 ps mainly results from cation reorientation. Because the viscosities are low and cation modification does not substantially change the viscosity, these ILs are interesting candidates for testing hydrodynamic models of rotational dynamics. The calculated hydrodynamic volumes are extraordinarily low, and roughly agree with values calculated from literature data for ILs with the same cations, but different anions. Comparison with magnetic relaxation data shows that the peculiarities are founded in the rotational dynamics and are not special to dielectric relaxation. Collectively, the observations make a strong case against the applicability of hydrodynamic approaches to the orientational dynamics of ions.
我们报告了六种同系离子液体（ILs）的介电弛豫谱，它们具有四（六氟异丙氧基）铝酸根 (Al(hfip)(4)) 作为常见阴离子。在几百皮秒的时间尺度上起主要作用的模式主要来自于阳离子的重排。由于这些 ILs 的粘度较低，而且阳离子的修饰并没有实质性地改变粘度，因此它们是测试旋转动力学流体力学模型的有趣候选物。计算得到的流体力学体积非常低，并且大致与具有相同阳离子但不同阴离子的 ILs 的文献数据计算值相符。与磁弛豫数据的比较表明，这些特性源于旋转动力学，而不是介电弛豫的特殊性。总的来说，这些观察结果强烈反对将流体力学方法应用于离子的取向动力学。
