Many-body System Laboratory, Department of Physics, National Chung-Cheng University, Chiayi 62102, Taiwan (R.O.C.).
Phys Rev E. 2017 Dec;96(6-1):062601. doi: 10.1103/PhysRevE.96.062601. Epub 2017 Dec 1.
The mesoscopic collective motion of self-propelling active particle suspension is experimentally investigated. The active particles are silica micro spheres with Au hemisphere coating, and their propelling strength is activated by laser irradiation. The suspension is driven from equilibrium to near equilibrium and far from equilibrium by tuning the excitation laser intensity. By use of the long-term particle tracking technique, the time evolution of a large amount of active particles is resolvable. For low laser intensity, the suspension is driven to near equilibrium state with homogeneous superdiffusion motion. The strength of enhanced superdiffusion is monotonically related to the laser intensity. For high laser intensity, the motility-induced phase separation with the coexistence of dense cluster and very dilute individual particle are observed. It leads to highly heterogeneous dynamic with less mobile jammed cluster and fast-moving particles and subsequently suppresses the enhanced superdiffusion. Such heterogeneous dynamics is similar to many far from equilibrium systems. Finally, the degree away from equilibrium (Gaussian dynamics) triggered by propelling strength is quantified by non-Gaussian parameters.
我们对自推进活性粒子悬浮液的介观集体运动进行了实验研究。活性粒子是具有 Au 半球形涂层的二氧化硅微球，它们的推进力通过激光照射激活。通过调节激发激光强度，将悬浮液从平衡驱动到近平衡和远离平衡。通过使用长期粒子跟踪技术，可以分辨出大量活性粒子的时间演化。对于低激光强度，悬浮液被驱动到具有均匀超扩散运动的近平衡状态。增强超扩散的强度与激光强度单调相关。对于高激光强度，观察到了具有密集簇和非常稀有的单个粒子共存的运动诱导相分离。这导致了高度非均匀的动力学，其中包括流动性较差的堵塞簇和快速移动的粒子，并随后抑制了增强的超扩散。这种非均匀动力学类似于许多远离平衡的系统。最后，通过非高斯参数量化了由推进力引发的远离平衡程度（高斯动力学）。
