Department of Theoretical Physics and Center for Biophysics, Saarland University, Saarbrücken 66123, Germany.
Phys Rev Lett. 2020 Jan 31;124(4):048001. doi: 10.1103/PhysRevLett.124.048001.
We study the capacity of active matter to rise in thin tubes against gravity and other related phenomena like wetting of vertical plates and spontaneous imbibition, where a wetting liquid is drawn into a porous medium. This capillary action or capillarity is well known in classical fluids and originates from attractive interactions between the liquid molecules and the container walls, and from the attraction of the liquid molecules among each other. We observe capillarity in a minimal model for scalar active matter with purely repulsive interactions, where an effective attraction emerges due to slowdown during collisions between active particles and between active particles and walls. Simulations indicate that the capillary rise in thin tubes is approximately proportional to the active sedimentation length λ and that the wetting height of a vertical plate grows superlinear with λ. In a disordered porous medium the imbibition height scales as ⟨h⟩∝λϕ_{m}, where ϕ_{m} is its packing fraction. These predictions are highly relevant for suspensions of sedimenting active colloids or motile bacteria in a porous medium under the influence of a constant force field.
我们研究了在重力和其他相关现象（如润湿垂直板和自发吸液）作用下，活性物质在细管中上升的能力，在这些现象中，润湿液体被吸入多孔介质中。这种毛细作用或毛细现象在经典流体中是众所周知的，它源于液体分子与容器壁之间的吸引力以及液体分子之间的吸引力。我们在具有纯排斥相互作用的标量活性物质的最小模型中观察到了毛细作用，其中由于活性粒子之间以及活性粒子与壁之间的碰撞减速，会出现有效吸引力。模拟表明，在细管中毛细上升与活性沉降长度 λ 大致成正比，并且垂直板的润湿高度与 λ 呈超线性增长。在无序多孔介质中，吸液高度的标度为 ⟨h⟩∝λϕ_{m}，其中 ϕ_{m} 是其堆积分数。这些预测对于在恒定力场作用下，沉降活性胶体或运动细菌在多孔介质中的悬浮液具有重要意义。
