Sehnem André Luiz, Niether Doreen, Wiegand Simone, Figueiredo Neto Antônio Martins
Institute of Physics , University of São Paulo , São Paulo , Brazil.
ICS-3 Soft Condensed Matter , Forschungszentrum Jülich GmbH , D-52428 Jülich , Germany.
J Phys Chem B. 2018 Apr 12;122(14):4093-4100. doi: 10.1021/acs.jpcb.8b01152. Epub 2018 Mar 30.
The ionic Soret effect induced by temperature gradients is investigated in organic electrolytes (tetramethylammonium and tetrabutylammonium hydroxides) dispersed in water using a holographic grating experiment. We report the influences of temperature and salt concentrations on the Soret, diffusion, and thermal diffusion coefficients. Experimental results to the thermal diffusion coefficient are compared with a theoretical description for thermodiffusion of Brownian particles in liquids based in the thermal expansion of the liquid solution. It is observed that the obtained thermal diffusion coefficients for the organic electrolytes present a similar temperature dependence as the theoretical prediction. Comparing the experimental results for the organic and common inorganic salts it is proposed an additional physical mechanism as the cause to the different thermal diffusion coefficients in both types of salt. We propose that the temperature dependence of hydration free energy gives rise to a force term that also leads to ion migration in a temperature gradient. We describe the thermal diffusion results as a competition between thermal expansion and hydration effects. The specific structure each type of ion cause in water molecules is considered in the heat of transport theory to describe thermal diffusion of electrolytes. A qualitative agreement is seen between our results and the classical heat of transport theory.
利用全息光栅实验，研究了分散在水中的有机电解质（氢氧化四甲铵和氢氧化四丁铵）中由温度梯度引起的离子索雷特效应。我们报告了温度和盐浓度对索雷特系数、扩散系数和热扩散系数的影响。将热扩散系数的实验结果与基于液体溶液热膨胀的布朗粒子在液体中热扩散的理论描述进行了比较。观察到有机电解质获得的热扩散系数呈现出与理论预测相似的温度依赖性。通过比较有机盐和常见无机盐的实验结果，提出了一种额外的物理机制，作为两种类型盐中热扩散系数不同的原因。我们提出，水化自由能的温度依赖性产生了一个力项，该力项也导致离子在温度梯度中迁移。我们将热扩散结果描述为热膨胀和水化效应之间的竞争。在输运热理论中考虑了每种离子在水分子中引起的特定结构，以描述电解质的热扩散。我们的结果与经典输运热理论之间存在定性的一致性。
