Katuri Jaideep, Poehnl Ruben, Sokolov Andrey, Uspal William, Snezhko Alexey
Argonne National Laboratory, 9700 S. Cass Avenue, Lemont, IL 60439, USA.
Department of Mechanical Engineering, University of Hawai'i at Mānoa, 2540 Dole Street, Holmes Hall 302, Honolulu, HI 96822, USA.
Sci Adv. 2022 Jul;8(26):eabo3604. doi: 10.1126/sciadv.abo3604. Epub 2022 Jul 1.
The emergence of large-scale collective phenomena from simple interactions between individual units is a hallmark of active matter systems. Active colloids with alignment-dominated interparticle interactions tend to develop orientational order and form motile coherent states, such as flocks and swarms. Alternatively, a combination of self-propulsion and excluded-volume interactions results in self-trapping and active phase separation into dense clusters. Here, we reveal unconventional arrested-motility states in ensembles of active discoidal particles powered by induced-charge electrophoresis. Combining experiments and computational modeling, we demonstrate that the shape asymmetry of the particles promotes the hydrodynamically assisted formation of active particles' bound states in a certain range of excitation parameters, ultimately leading to a spontaneous collective state with arrested motility. Unlike the jammed clusters obtained through self-trapping, the arrested-motility phase remains sparse, dynamic, and reconfigurable. The demonstrated mechanism of phase separation seeded by bound state formation in ensembles of oblate active particles is generic and should be applicable to other active colloidal systems.
从单个单元之间的简单相互作用中出现大规模集体现象是活性物质系统的一个标志。具有以排列为主导的粒子间相互作用的活性胶体倾向于发展取向有序并形成运动相干态，如群聚和蜂群。另外，自推进和排阻体积相互作用的结合会导致自捕获和活性相分离成密集簇。在这里，我们揭示了由感应电荷电泳驱动的活性盘状粒子集合体中非常规的运动停滞状态。结合实验和计算建模，我们证明了粒子的形状不对称在一定范围的激发参数下促进了活性粒子束缚态的流体动力学辅助形成，最终导致具有运动停滞的自发集体状态。与通过自捕获获得的堵塞簇不同，运动停滞相仍然稀疏、动态且可重构。在扁球形活性粒子集合体中由束缚态形成引发的相分离机制是通用的，应该适用于其他活性胶体系统。
