Laboratoire Ondes et Matière d'Aquitaine, Université de Bordeaux & CNRS, 33405 Talence, France.
Phys Rev Lett. 2016 Apr 1;116(13):138302. doi: 10.1103/PhysRevLett.116.138302. Epub 2016 Mar 30.
We study hydrodynamic slowing down of a particle moving in a temperature gradient perpendicular to a wall. At distances much smaller than the particle radius, h≪a, the lubrication approximation leads to the reduced velocity u/u_{0}=3(h/a)[ln(a/h)-9/4], where u_{0} is the velocity in the bulk. With Brenner's result for confined diffusion, we find that the trapping efficiency, or effective Soret coefficient, increases logarithmically as the particle gets very close to the wall. Our results provide a quantitative explanation for the recently observed enhancement of thermophoretic trapping at short distances. Our discussion of parallel and perpendicular thermophoresis in a capillary reveals a good agreement with experiments on charged polystyrene particles, and sheds some light on a controversy concerning the size dependence and the nonequilibrium nature of the Soret effect.
我们研究了垂直于壁面的温度梯度中运动粒子的流体动力减速。在远小于粒子半径的距离处，h≪a，润滑近似导致速度降低为 u/u_{0}=3(h/a)[ln(a/h)-9/4]，其中 u_{0}是在体相中的速度。结合 Brenner 的受限扩散结果，我们发现随着粒子非常接近壁面，捕获效率或有效 Soret 系数呈对数增加。我们的结果为最近观察到的短距离热泳捕获增强提供了定量解释。我们对毛细管中平行和垂直热泳的讨论与带电聚苯乙烯粒子的实验很好地吻合，并为关于 Soret 效应的尺寸依赖性和非平衡性质的争议提供了一些启示。
