Johari G P, Andersson Ove
Department of Materials Science and Engineering, McMaster University, Hamilton, Ontario L8S 4L7, Canada.
J Chem Phys. 2006 Sep 28;125(12):124501. doi: 10.1063/1.2353833.
The long-known observations that dc conductivity sigma(dc) of an ultraviscous liquid varies nonlinearly with the dielectric relaxation time tau, and the slope of the log sigma(dc) against log tau plot deviates from -1 are currently seen as two of the violations of the Debye-Stokes-Einstein equation. Here we provide a formalism using a zeroth order Bjerrum description for ion association to show that in addition to its variation with temperature T and pressure P, impurity ion population varies with a liquid's equilibrium dielectric permittivity. Inclusion of this electrostatic effect modifies the Debye-Stokes-Einstein equation to log(sigma(dc)tau)=constant+log alpha, where alpha is the T and P-dependent degree of ionic dissociation of an electrolytic impurity. Variation of a liquid's shear modulus with T and P would add to the nonlinearity of sigma(dc)-tau relation, as would a nonequivalence of the shear and dielectric relaxation times, proton transfer along the hydrogen bonds, or occurrence of another chemical process. This is illustrated by using the data for ultraviscous acetaminophen-aspirin liquid.
长期以来已知的观察结果表明，超粘性液体的直流电导率σ(dc)随介电弛豫时间τ呈非线性变化，并且log σ(dc) 对log τ的图线斜率偏离-1，目前这被视为对德拜-斯托克斯-爱因斯坦方程的两种违背情况。在此，我们提供一种形式体系，使用离子缔合的零阶比耶鲁姆描述来表明，除了随温度T和压力P变化外，杂质离子数量还随液体的平衡介电常数而变化。纳入这种静电效应会将德拜-斯托克斯-爱因斯坦方程修改为log(σ(dc)τ)=常数 + log α，其中α是与T和P相关的电解杂质的离子解离度。液体剪切模量随T和P的变化会增加σ(dc)-τ关系的非线性，剪切弛豫时间和介电弛豫时间的不等效、质子沿氢键的转移或另一个化学过程的发生也会如此。通过使用超粘性对乙酰氨基酚-阿司匹林液体的数据对此进行了说明。
