Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, USA.
Basque Center for Applied Mathematics (BCAM), Mazarredo 14, E48009 Bilbao, Basque Country-Spain.
Sci Adv. 2023 Mar 10;9(10):eade0320. doi: 10.1126/sciadv.ade0320. Epub 2023 Mar 8.
It is known that obstacles can hydrodynamically trap bacteria and synthetic microswimmers in orbits, where the trapping time heavily depends on the swimmer flow field and noise is needed to escape the trap. Here, we use experiments and simulations to investigate the trapping of microrollers by obstacles. Microrollers are rotating particles close to a bottom surface, which have a prescribed propulsion direction imposed by an external rotating magnetic field. The flow field that drives their motion is quite different from previously studied swimmers. We found that the trapping time can be controlled by modifying the obstacle size or the colloid-obstacle repulsive potential. We detail the mechanisms of the trapping and find two remarkable features: The microroller is confined in the wake of the obstacle, and it can only enter the trap with Brownian motion. While noise is usually needed to escape traps in dynamical systems, here, we show that it is the only means to reach the hydrodynamic attractor.
众所周知，障碍物可以通过水动力将细菌和合成微游泳者困在轨道中，而被困的时间主要取决于游泳者的流场，并且需要噪声才能逃脱陷阱。在这里，我们使用实验和模拟来研究障碍物对微滚轮的捕获。微滚轮是接近底部表面的旋转颗粒，它们具有由外部旋转磁场施加的预定推进方向。驱动其运动的流场与以前研究过的游泳者非常不同。我们发现，通过修改障碍物的大小或胶体-障碍物排斥势，可以控制被困时间。我们详细研究了捕获的机制，并发现了两个显著的特点：微滚轮被限制在障碍物的尾流中，并且只能通过布朗运动进入陷阱。虽然在动力系统中通常需要噪声来逃脱陷阱，但在这里，我们表明这是到达水动力吸引子的唯一途径。
