Power G, Vij J K, Johari G P
Laboratory of Advanced Materials, Department of Electronic Engineering, Trinity College, University of Dublin, Dublin 2, Ireland.
J Phys Chem B. 2007 Sep 27;111(38):11201-8. doi: 10.1021/jp072268j. Epub 2007 Sep 1.
The basis for a modification of the Debye-Stokes-Einstein (DSE) equation between the dc conductivity, sigma(dc), and dielectric relaxation time, tau, has been examined by using broad-band dielectric spectroscopy of LiClO4 solutions in 5-methyl-2-hexanol and 1-propanol and of pure liquids. According to the DSE equation, the log sigma(dc)-log tau plots should have a slope of -1. We find that sigma(dc) begins to depend upon the structure of an electrolytic solution when a variation of solvent's equilibrium dielectric permittivity, epsilon(s), with temperature causes the ion population to vary. As a consequence of this intrinsic dependence, the log sigma(dc)-log tau plots do not obey the DSE equation. Inclusion of the effect of change in epsilon(s) on the DSE equation may be useful in analyzing the measured quantities in terms of Brownian diffusion of both ions and molecules in ultraviscous liquids. Proton translocation along a hydrogen bond contributes little to sigma(dc), which appears to be predominantly determined by the ion population in the two alcohols and the solutions. The effect is briefly discussed in the potential energy landscape paradigm of structure fluctuations, and it is suggested that the high-frequency shear modulus measurements of ionic solutions would help reveal the temperature-dependent deviation from the DSE equation.
通过对LiClO₄在5-甲基-2-己醇和1-丙醇中的溶液以及纯液体进行宽带介电谱研究，考察了德拜-斯托克斯-爱因斯坦（DSE）方程在直流电导率σ(dc)和介电弛豫时间τ之间修正的依据。根据DSE方程，log σ(dc)-log τ图的斜率应为-1。我们发现，当溶剂的平衡介电常数ε(s)随温度变化导致离子数量改变时，σ(dc)开始依赖于电解质溶液的结构。由于这种内在依赖性，log σ(dc)-log τ图不符合DSE方程。将ε(s)变化的影响纳入DSE方程，可能有助于根据超粘性液体中离子和分子的布朗扩散来分析测量量。质子沿氢键的迁移对σ(dc)贡献很小，σ(dc)似乎主要由两种醇及其溶液中的离子数量决定。在结构涨落的势能景观范式中简要讨论了该效应，并提出离子溶液的高频剪切模量测量将有助于揭示与DSE方程的温度依赖性偏差。
