Hokmabad Babak Vajdi, Nishide Akinori, Ramesh Prashanth, Krüger Carsten, Maass Corinna C
Max Planck Institute for Dynamics and Self-Organization, Am Faßberg 17, 37077 Göttingen, Germany.
Institute for the Dynamics of Complex Systems, Georg August Universität, Göttingen, Germany.
Soft Matter. 2022 Apr 6;18(14):2731-2741. doi: 10.1039/d1sm01795k.
We report on the emergence of spontaneously rotating clusters in active emulsions. Ensembles of self-propelling droplets sediment and then self-organise into planar, hexagonally ordered clusters which hover over the container bottom while spinning around the plane normal. This effect exists for symmetric and asymmetric arrangements of isotropic droplets and is therefore not caused by torques due to geometric asymmetries. We found, however, that individual droplets exhibit a helical swimming mode in a small window of intermediate activity in a force-free bulk medium. We show that by forming an ordered cluster, the droplets cooperatively suppress their chaotic dynamics and turn the transient instability into a steady rotational state. We analyse the collective rotational dynamics as a function of droplet activity and cluster size and further propose that the stable collective rotation in the cluster is caused by a cooperative coupling between the rotational modes of individual droplets in the cluster.
我们报告了活性乳液中自发旋转簇的出现。自推进液滴的集合体沉降，然后自组织成平面的、六边形有序的簇，这些簇在容器底部上方盘旋，同时绕平面法线旋转。这种效应在各向同性液滴的对称和不对称排列中都存在，因此不是由几何不对称引起的扭矩导致的。然而，我们发现，在无外力的本体介质中，单个液滴在中等活性的小窗口内表现出螺旋游动模式。我们表明，通过形成有序簇，液滴协同抑制其混沌动力学，并将瞬态不稳定性转变为稳定的旋转状态。我们分析了集体旋转动力学作为液滴活性和簇大小的函数，并进一步提出簇中稳定的集体旋转是由簇中单个液滴的旋转模式之间的协同耦合引起的。
