CAS Key Laboratory of Mechanical Behavior and Design of Materials, Department of Modern Mechanics, CAS Center for Excellence in Complex System Mechanics, University of Science and Technology of China, Hefei, Anhui 230026, China.
Soft Matter. 2023 May 3;19(17):3222-3227. doi: 10.1039/d2sm01243j.
Active particles without detailed balance can rectify their random motions to drive the directed movement or rotation of asymmetric passive obstacles. However, whether they can drive the directed movement of symmetric passive obstacles is still unclear. Here, we show that a rod-like passive particle which is fixed to move along the -axis in an active bath can keep long-lived directed movement at nearly constant speed due to the spontaneous symmetry breaking of the neighboring active particle cluster. If the passive particle is further confined by a harmonic potential, it may undergo self-sustained periodic oscillation for an appropriate length of the passive particle and self-propelled velocity of active particles. The restoring force from the harmonic potential will trigger the velocity jump-off and thus lead to self-sustained periodic oscillation. Remarkably, the relationship between the velocity of the passive particle and the external force shows that the effective viscosity of the active bath may become negative in some regime. Finally, we develop a minimum 1D theoretical model to further probe the mechanism underlying the directed movement and self-sustained oscillation of the passive particle. Our findings reveal the effect of the moving boundary on the active bath and demonstrate a novel method to extract practical mechanical work from the active bath to propel microdevices.
无详细平衡的活性粒子可以纠正其随机运动，从而驱动不对称的被动障碍物的定向运动或旋转。然而，它们是否能驱动对称的被动障碍物的定向运动尚不清楚。在这里，我们表明，由于相邻活性粒子簇的自发对称破缺，固定在活性浴中沿 x 轴运动的棒状被动粒子可以保持长寿命的定向运动，速度几乎恒定。如果将被动粒子进一步限制在简谐势中，它可能会经历自维持的周期性振荡，对于适当长度的被动粒子和主动粒子的自推进速度。简谐势的恢复力将引发速度跳跃，从而导致自维持的周期性振荡。值得注意的是，被动粒子速度与外力之间的关系表明，在某些情况下，活性浴的有效粘度可能变为负值。最后，我们开发了一个最小的 1D 理论模型，以进一步探究被动粒子定向运动和自维持振荡的机制。我们的发现揭示了移动边界对活性浴的影响，并展示了一种从活性浴中提取实用机械功以推动微器件的新方法。
