微辊形成的不稳定锋和稳定“生物”
Unstable fronts and stable "critters" formed by microrollers
摘要：
在平衡和驱动系统中，物体凝聚成稳定的团簇是自然发生的。人们通常认为，潜在的相互作用，耗尽力，或传感是唯一的机制，可以创建长寿命的紧凑结构。在这里，我们表明，持久的能动结构可以自发地形成单独的流体动力学相互作用，没有传感或潜在的相互作用。我们研究了这种结构的形成在一个系统的胶体辊悬浮和平移以上的地板，使用实验和大规模的三维模拟。在这个系统中，簇起源于以前未报道的指状不稳定性，指状不稳定性从不稳定的前端夹断，形成自主的“生物”，其大小由颗粒在地板上方的高度选择。这些生物是系统的稳定状态，比单个粒子移动得快得多，并迅速响应不断变化的驱动器。通过旋转磁场设定速度和方向，这些活性结构为微尺度的引导运输、流动产生和混合提供了有趣的可能性。
英文摘要：
Condensation of objects into stable clusters occurs naturally in equilibrium and driven systems. It is commonly held that potential interactions, depletion forces, or sensing are the only mechanisms which can create long-lived compact structures. Here we show that persistent motile structures can form spontaneously from hydrodynamic interactions alone with no sensing or potential interactions. We study this structure formation in a system of colloidal rollers suspended and translating above a floor, using both experiments and large-scale 3D simulations. In this system, clusters originate from a previously unreported fingering instability, where fingers pinch off from an unstable front to form autonomous "critters", whose size is selected by the height of the particles above the floor. These critters are a stable state of the system, move much faster than individual particles, and quickly respond to a changing drive. With speed and direction set by a rotating magnetic field, these active structures offer interesting possibilities for guided transport, flow generation, and mixing at the microscale.
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