EAGER: Emergent order of hydrodynamically coupled microrotors

1544196（Vlahovska）拟议研究的目的是从理论上和实验上研究一类新的活性流体，即自旋转粒子悬浮液。活性流体是具有独特行为方式的流体，因为活性颗粒的存在可以自组装，或者可以以不同的方式移动和包装，从而赋予流体不同的宏观特性。某些复杂流体和生物流体属于这一类。即使是一群鸟或一群鱼，其中每一个运动的动物都在自己的运动，但所有的运动都遵循一个比个体大得多的模式，都是活动流体的例子。提出了研究旋转球体（转子）密集悬架的方法。最近发现，在初始随机分布的上下自旋的单层转子中，相同自旋的转子自发地分离并集体在交通车道上移动或在大涡流中循环。当转子密度接近最大填料时，转子会堵塞成不断融化、重组和移动的晶体。我们建议用计算和实验相结合的方法来研究这些现象，以了解这种集体行为是如何从转子之间的流体动力相互作用中产生的。数值模拟采用浸入边界法。实验系统依靠昆克效应，这是一个自发旋转的介电球在一个施加均匀电场。提出的研究旨在(1)将静电相互作用纳入数值模拟，(2)研究一对和单层Quincke转子的动力学。除了推进基础知识之外，该研究还将发现新的动态结构，可以用于设计响应外部环境的“智能”材料。pi将把这项研究的结果纳入研究生课程，并将利用布朗大学成功的外展项目，向公众传达这项工作的相关性和重要性。

1544196(Vlahovska)The objective of the proposed research is to investigate theoretically and experimentally a new class of active fluids, that of suspensions of self-rotating particles. Active fluids are fluids that behave in unique ways, because of the presence of active particles that can self-assemble, or can move and pack in different ways, giving different macroscopic properties to the fluid. Certain complex fluids and biofluids fall in this category. Even a flock of birds, or a school of fish, where each moving animal moves on its own, but the motion of all follows a pattern at a much larger scale than the individual, are examples of active fluids.It is proposed to examine dense suspensions of rotating spheres (rotors). It has very recently been found that in a monolayer of rotors with initially randomly distributed up or down spins, same-spin rotors spontaneously segregate and collectively move in traffic lanes or circulate in large vortices. When the rotor density gets close to maximum packing, the rotors jam into crystals that continuously melt, reassemble, and move. It is proposed to study these phenomena with a combined computational and experimental approach to understand how this collective behavior emerges from the hydrodynamic interactions between the rotors. The numerical simulations are based on the immersed boundary method. The experimental system relies on the Quincke effect, which is the spontaneous spinning of a dielectric sphere in an applied uniform electric field. The proposed research aims to (1) include the electrostatic interactions in the numerical simulations, and (2) investigate the dynamics of a pair and monolayer of Quincke rotors. In addition to advancing basic knowledge, the research will uncover novel dynamic structures that could be exploited for design of `smart' materials responsive to the external environment. The PIs will incorporate the results from this research in graduate courses and will also leverage successful outreach programs at Brown University to communicate the relevance and significance of the work to the general public.