Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.
Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.
ACS Nano. 2023 Apr 25;17(8):7911-7919. doi: 10.1021/acsnano.3c01966. Epub 2023 Apr 6.
The process of dynamic self-organization of small building blocks is fundamental to the emergent function of living systems and is characteristic of their out-of-equilibrium homeostasis. The ability to control the interactions of synthetic particles in large groups could lead to the realization of analogous macroscopic robotic systems with microscopic complexity. Rotationally induced self-organization has been observed in biological systems and modeled theoretically, but studies of fast, autonomously moving synthetic rotors remain rare. Here, we report switchable, out-of-equilibrium hydrodynamic assembly and phase separation in suspensions of acoustically powered chiral microspinners. Semiquantitative modeling suggests that three-dimensionally (3D) complex spinners interact through viscous and weakly inertial (streaming) flows. The interactions between spinners were studied over a range of densities to construct a phase diagram, which included gaseous dimer pairing at low density, collective rotation and multiphase separation at intermediate densities, and ultimately jamming at high density. The 3D chirality of the spinners leads to self-organization in parallel planes, forming a three-dimensionally hierarchical system that goes beyond the 2D systems that have so far been modeled computationally. Dense mixtures of spinners and passive tracer particles also show active-passive phase separation. These observations are consistent with recent theoretical predictions of the hydrodynamic coupling between rotlets generated by autonomous spinners and provide an exciting experimental window to the study of colloidal active matter and microrobotic systems.
小建筑块的动态自组织过程是生命系统涌现功能的基础，也是其非平衡稳态的特征。控制大量合成粒子相互作用的能力可能会导致类似的宏观机器人系统具有微观复杂性。在生物系统中已经观察到旋转诱导的自组织，并进行了理论建模，但快速、自主运动的合成转子的研究仍然很少。在这里，我们报告了在声驱动手性微旋转器悬浮液中可切换的、非平衡的流体动力学组装和相分离。半定量模型表明，三维（3D）复杂旋转器通过粘性和弱惯性（流动）流相互作用。在一系列密度下研究了旋转器之间的相互作用，以构建相图，其中包括低密度下的气态二聚体配对、中等密度下的集体旋转和多相分离，以及最终的高密度堵塞。旋转器的 3D 手性导致平行平面中的自组织，形成一个超越迄今为止在计算上建模的二维系统的三维层次系统。旋转器和无源示踪粒子的密集混合物也表现出主动-被动相分离。这些观察结果与自主旋转器产生的旋流之间的流体动力耦合的最新理论预测一致，并为胶体活性物质和微机器人系统的研究提供了一个令人兴奋的实验窗口。
