Institut für Theoretische Physik II: Weiche Materie, Heinrich-Heine-Universität Düsseldorf, Universitätsstraße 1, D-40225, Düsseldorf, Germany.
J Chem Phys. 2012 Apr 7;136(13):134106. doi: 10.1063/1.3698622.
A binary mixture of particles interacting via long-ranged repulsive forces is studied in gravity by computer simulation and theory. The more repulsive A-particles create a depletion zone of less repulsive B-particles around them reminiscent to a bubble. Applying Archimedes' principle effectively to this bubble, an A-particle can be lifted in a fluid background of B-particles. This "depletion bubble" mechanism explains and predicts a brazil-nut effect where the heavier A-particles float on top of the lighter B-particles. It also implies an effective attraction of an A-particle towards a hard container bottom wall which leads to boundary layering of A-particles. Additionally, we have studied a periodic inversion of gravity causing perpetuous mutual penetration of the mixture in a slit geometry. In this nonequilibrium case of time-dependent gravity, the boundary layering persists. Our results are based on computer simulations and density functional theory of a two-dimensional binary mixture of colloidal repulsive dipoles. The predicted effects also occur for other long-ranged repulsive interactions and in three spatial dimensions. They are therefore verifiable in settling experiments on dipolar or charged colloidal mixtures as well as in charged granulates and dusty plasmas.
通过计算机模拟和理论研究，研究了在重力作用下通过长程斥力相互作用的粒子二元混合物。更具排斥性的 A 粒子在其周围形成了一个排斥性较弱的 B 粒子耗尽区，类似于气泡。将阿基米德原理有效地应用于这个气泡，一个 A 粒子可以在 B 粒子的流体背景中被提升。这种“耗尽气泡”机制解释并预测了较重的 A 粒子漂浮在较轻的 B 粒子上的巴西坚果效应。它还暗示了 A 粒子对硬容器底壁的有效吸引力，导致 A 粒子的边界分层。此外，我们还研究了重力的周期性反转，导致混合物在狭缝几何形状中不断相互渗透。在这种依赖于时间的非平衡重力情况下，边界分层仍然存在。我们的结果基于胶体排斥偶极子二维二元混合物的计算机模拟和密度泛函理论。预测的效果也适用于其他长程排斥相互作用和三维空间。因此，它们可以在关于偶极子或带电胶体混合物的沉降实验以及带电颗粒和尘埃等离子体中得到验证。
