Zhang Bo, Karani Hamid, Vlahovska Petia M, Snezhko Alexey
Materials Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, IL 60439, USA.
Engineering Sciences and Applied Mathematics, Northwestern University, Evanston, IL 60206, USA and Department of Physics, Brown University, Providence, RI 02912, USA.
Soft Matter. 2021 May 12;17(18):4818-4825. doi: 10.1039/d1sm00363a.
Active colloidal fluids, biological and synthetic, often demonstrate complex self-organization and the emergence of collective behavior. Spontaneous formation of multiple vortices has been recently observed in a variety of active matter systems, however, the generation and tunability of the active vortices not controlled by geometrical confinement remain challenging. Here, we exploit the persistence length of individual particles in ensembles of active rollers to tune the formation of vortices and to orchestrate their characteristic sizes. We use two systems and employ two different approaches exploiting shape anisotropy or polarization memory of individual units for control of the persistence length. We characterize the dynamics of emergent multi-vortex states and reveal a direct link between the behavior of the persistence length and properties of the emergent vortices. We further demonstrate common features between the two systems including anti-ferromagnetic ordering of the neighboring vortices and active turbulent behavior with a characteristic energy cascade in the particles velocity field energy spectra. Our findings provide insights into the onset of spatiotemporal coherence in active roller systems and suggest a control knob for manipulation of dynamic self-assembly in active colloidal ensembles.
活性胶体流体，包括生物和合成的，常常表现出复杂的自组织和集体行为的出现。最近在各种活性物质系统中都观察到了多个涡旋的自发形成，然而，不受几何限制控制的活性涡旋的产生和可调性仍然具有挑战性。在这里，我们利用活性滚动体集合中单个粒子的持久长度来调节涡旋的形成并协调它们的特征尺寸。我们使用两个系统，并采用两种不同的方法，利用单个单元的形状各向异性或极化记忆来控制持久长度。我们表征了涌现的多涡旋态的动力学，并揭示了持久长度的行为与涌现涡旋的性质之间的直接联系。我们进一步证明了这两个系统之间的共同特征，包括相邻涡旋的反铁磁有序以及粒子速度场能谱中具有特征能量级联的活性湍流行为。我们的发现为活性滚动体系统中时空相干性的起始提供了见解，并提出了一个用于操纵活性胶体集合中动态自组装的控制旋钮。
