流体动力学相互作用微游泳体的相分离与共存
Phase Separation and Coexistence of Hydrodynamically Interacting Microswimmers
摘要：
球形微泳者的集体行为的一个显著特征是，对于足够强的自推进，它们相分离成与低密度无序环境共存的密集簇。扩展我们以前的工作，我们使用的蠕动作为一个模型的游泳者和基于粒子的多粒子碰撞动力学模拟方法，探讨流体力学的影响，他们的相行为在准二维几何形状。的粗化动力学的相分离状态是扩散的中间时间制度，然后由最后的弹道致密化的致密集群。我们确定了Péclet数与密度的相图中的双结点线。有趣的是，随着平均密度或致密团簇尺寸的增加，气体双节点会向更小的密度移动，我们使用最近引入的压力平衡来解释[S。C. Takatori等人，物理修订信函113，028103（2014）]通过流体动力学贡献扩展。此外，我们发现，对于推和拉的双节线转移到更大的Péclet数相比，中性蠕动。最后，当降低Péclet数时，致密相从六方“固体”转变为无序的“流体”状态。
英文摘要：
A striking feature of the collective behavior of spherical microswimmers is that for sufficiently strong self-propulsion they phase-separate into a dense cluster coexisting with a low-density dis- ordered surrounding. Extending our previous work, we use the squirmer as a model swimmer and the particle-based simulation method of multi-particle collision dynamics to explore the influence of hydrodynamics on their phase behavior in a quasi-two-dimensional geometry. The coarsening dynamics towards the phase-separated state is diffusive in an intermediate time regime followed by a final ballistic compactification of the dense cluster. We determine the binodal lines in a phase diagram of Péclet number versus density. Interestingly, the gas binodals are shifted to smaller densities for increasing mean density or dense-cluster size, which we explain using a recently introduced pressure balance [S. C. Takatori et al., Phys. Rev. Lett. 113, 028103 (2014)] extended by a hydrodynamic contribution. Furthermore, we find that for pushers and pullers the binodal line is shifted to larger Péclet numbers compared to neutral squirmers. Finally, when lowering the Péclet number, the dense phase transforms from a hexagonal "solid" to a disordered "fluid" state.
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