Sassa Yuriko, Shibata Shuhei, Iwashita Yasutaka, Kimura Yasuyuki
Department of Physics, School of Sciences, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.
Phys Rev E Stat Nonlin Soft Matter Phys. 2012 Jun;85(6 Pt 1):061402. doi: 10.1103/PhysRevE.85.061402. Epub 2012 Jun 1.
We experimentally study the motion of optically driven colloidal particles on a circular path by varying their number N. Although an identical driving force is applied to each particle, their equally spaced configuration is hydrodynamically unstable, and a doublet configuration is spontaneously formed. In small-N systems, the angular difference between neighboring particles exhibits oscillatory or nonoscillatory behavior. The number of oscillatory modes that appear depends on the maximum number of doublets that the system can contain. Frequent switching between different modes was observed with increasing N. The characteristic frequencies of the oscillatory modes are discussed theoretically by linear stability analysis of the equations that govern the motion of hydrodynamically coupled particles. The evaluated frequencies of the slowest modes exhibit reasonably good agreement with those of the mainly observed modes in experiments. The relationship between the characteristic frequencies and specific configurations is confirmed experimentally by setting a specific initial configuration for the particles. An increase in N also enhances the mean angular velocity of the particles owing to the reduced effective viscosity in large-N systems.
我们通过改变光学驱动的胶体粒子的数量N，对其在圆形路径上的运动进行了实验研究。尽管对每个粒子施加了相同的驱动力，但它们等间距的构型在流体动力学上是不稳定的，并且会自发形成双峰构型。在小N系统中，相邻粒子之间的角差表现出振荡或非振荡行为。出现的振荡模式数量取决于系统能够包含的最大双峰数量。随着N的增加，观察到不同模式之间频繁切换。通过对控制流体动力学耦合粒子运动的方程进行线性稳定性分析，从理论上讨论了振荡模式的特征频率。评估出的最慢模式的频率与实验中主要观察到的模式的频率表现出合理的良好一致性。通过为粒子设置特定的初始构型，从实验上证实了特征频率与特定构型之间的关系。由于大N系统中有效粘度的降低，N的增加也提高了粒子的平均角速度。
