Biocolloid and Fluid Physics Research Group, Departamento de Física Aplicada, Facultad de Ciencias, Universidad de Granada, Campus Fuentenueva S/N, 18071 Granada, Spain.
J Chem Phys. 2012 Feb 14;136(6):064517. doi: 10.1063/1.3685101.
We study how varying the Péclet number (Pe) affects the steady state sedimentation of colloidal particles that interact through short-ranged attractions. By employing a hybrid molecular dynamics simulation method we demonstrate that the average sedimentation velocity changes from a non-monotonic dependence on packing fraction φ at low Pe numbers, to a monotonic decrease with φ at higher Pe numbers. At low Pe number the pair correlation functions are close to their equilibrium values, but as the Pe number increases, important deviations from equilibrium forms are observed. Although the attractive forces we employ are not strong enough to form permanent clusters, they do induce transient clusters whose behaviour is also affected by Pe number. In particular, clusters are more likely to fragment and less likely to aggregate at larger Pe numbers, and the probability of finding larger clusters decreases with increasing Pe number. Interestingly, the lifetime of the clusters is more or less independent of Pe number in the range we study. Instead, the change in cluster distribution occurs because larger clusters are less likely to form with increasing Pe number. These results illustrate some of the subtleties that occur in the crossover from equilibrium like to purely non-equilibrium behaviour as the balance between convective and thermal forces changes.
我们研究了通过改变 Peclet 数 (Pe) 如何影响通过短程吸引力相互作用的胶体颗粒的稳态沉降。通过采用混合分子动力学模拟方法，我们证明了平均沉降速度在低 Pe 数时，从对填充分数 φ 的非单调依赖关系变为在更高的 Pe 数时与 φ 的单调下降。在低 Pe 数时，对关联函数接近它们的平衡值，但随着 Pe 数的增加，观察到与平衡形式的重要偏差。虽然我们使用的吸引力不够强以形成永久团簇，但它们确实会诱导瞬态团簇，其行为也受到 Pe 数的影响。特别是，在更大的 Pe 数下，团簇更容易发生碎片，而不太可能聚集，并且随着 Pe 数的增加，发现更大团簇的概率降低。有趣的是，在我们研究的范围内，团簇的寿命或多或少独立于 Pe 数。相反，由于随着 Pe 数的增加，较大的团簇不太可能形成，因此团簇的分布发生了变化。这些结果说明了在从平衡态到纯非平衡态的转变中发生的一些微妙之处，因为对流和热力之间的平衡发生了变化。
