Ripoll M, Mussawisade K, Winkler R G, Gompper G
Institut für Festkörperforschung, Forschungszentrum Jülich, D-52425 Jülich, Germany.
Phys Rev E Stat Nonlin Soft Matter Phys. 2005 Jul;72(1 Pt 2):016701. doi: 10.1103/PhysRevE.72.016701. Epub 2005 Jul 5.
We investigate the hydrodynamic properties of a fluid simulated with a mesoscopic solvent model. Two distinct regimes are identified, the "particle regime" in which the dynamics is gaslike and the "collective regime" where the dynamics is fluidlike. This behavior can be characterized by the Schmidt number, which measures the ratio between viscous and diffusive transport. Analytical expressions for the tracer diffusion coefficient, which have been derived on the basis of a molecular-chaos assumption, are found to describe the simulation data very well in the particle regime, but important deviations are found in the collective regime. These deviations are due to hydrodynamic correlations. The model is then extended in order to investigate self-diffusion in colloidal dispersions. We study first the transport properties of heavy pointlike particles in the mesoscopic solvent, as a function of their mass and number density. Second, we introduce excluded-volume interactions among the colloidal particles and determine the dependence of the diffusion coefficient on the colloidal volume fraction for different solvent mean-free paths. In the collective regime, the results are found to be in good agreement with previous theoretical predictions based on Stokes hydrodynamics and the Smoluchowski equation.
我们研究了用介观溶剂模型模拟的流体的流体动力学性质。确定了两种不同的状态，即动力学呈气体状的“粒子状态”和动力学呈流体状的“集体状态”。这种行为可以用施密特数来表征，它衡量粘性输运和扩散输运之间的比率。基于分子混沌假设推导得到的示踪扩散系数的解析表达式，在粒子状态下能很好地描述模拟数据，但在集体状态下发现了重要偏差。这些偏差是由于流体动力学相关性造成的。然后扩展该模型以研究胶体分散体中的自扩散。我们首先研究重的点状粒子在介观溶剂中的输运性质，作为其质量和数密度的函数。其次，我们引入胶体粒子之间的排除体积相互作用，并确定不同溶剂平均自由程下扩散系数对胶体体积分数的依赖性。在集体状态下，结果与先前基于斯托克斯流体动力学和斯莫卢霍夫斯基方程的理论预测高度吻合。
