Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada.
J Chem Phys. 2011 Mar 21;134(11):114310. doi: 10.1063/1.3562369.
A study is presented of tracer diffusion in a rough hard sphere fluid. Unlike smooth hard spheres, collisions between rough hard spheres can exchange rotational and translational energy and momentum. It is expected that as tracer particles become larger, their diffusion constants will tend toward the Stokes-Einstein hydrodynamic result. It has already been shown that in this limit, smooth hard spheres adopt "slip" boundary conditions. The current results show that rough hard spheres adopt boundary conditions proportional to the degree of translational-rotational energy exchange. Spheres for which this exchange is the largest adopt "stick" boundary conditions while those with more intermediate exchange adopt values between the "slip" and "stick" limits. This dependence is found to be almost linear. As well, changes in the diffusion constants as a function of this exchange are examined and it is found that the dependence is stronger than that suggested by the low-density, Boltzmann result. Compared with smooth hard spheres, real molecules undergo inelastic collisions and have attractive wells. Rough hard spheres model the effect of inelasticity and show that even without the presence of attractive forces, the boundary conditions for large particles can deviate from "slip" and approach "stick."
研究了粗糙硬球流体中的示踪扩散。与光滑硬球不同，粗糙硬球之间的碰撞可以交换转动和平移能量和动量。预计随着示踪粒子的增大，它们的扩散常数将趋于斯托克斯-爱因斯坦流体力学结果。已经表明，在这个极限下，光滑硬球采用“滑移”边界条件。当前的结果表明，粗糙硬球采用与平移-转动能量交换程度成正比的边界条件。对于这种交换最大的球体采用“固着”边界条件，而那些具有更多中间交换的球体采用“滑移”和“固着”之间的边界条件。这种依赖性几乎是线性的。此外，还研究了扩散常数随这种交换的变化，发现这种依赖性比低密度、玻尔兹曼结果所暗示的要强。与光滑硬球相比，真实分子经历非弹性碰撞并有吸引力阱。粗糙硬球模型化了非弹性的影响，表明即使没有吸引力的存在，大粒子的边界条件也可以偏离“滑移”并接近“固着”。
