Mesoscopic turbulence and local order in Janus particles self-propelling under an ac electric field
Mesoscopic turbulence and local order in Janus particles self-propelling under an ac electric field
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DOI：
10.1103/physreve.92.052309
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发表时间：
2015-11-13
影响因子：
2.4
通讯作者：
Sano, Masaki
中科院分区：
文献类型：
--
作者：
Nishiguchi, Daiki;Sano, Masaki
为了阐明活性粒子表现出的介观湍流机制，我们实验研究了无生命自推进粒子的湍流状态。我们实现了一个在交流电场作用下二维表面上自推进的非对称胶体粒子（Janus粒子）稠密悬浮液的实验系统。拥挤情况下Janus粒子的速度场可以看作是一种湍流，因为它包含许多旋涡，它们的速度变化突然。它们的速度场相关函数揭示了极向和反平行向相互作用的共存，这被认为是引发介观湍流的原因。极性阶和向列阶局部序参数的概率分布表明粒子沿同一方向运动的局部团簇的形成。在观测到极向和星团形成的空间尺度上，速度场能谱出现一个宽峰。能量是在粒子尺度上注入的，像能量这样的守恒量可以级联到更大的簇中。
To elucidate mechanisms of mesoscopic turbulence exhibited by active particles, we experimentally study turbulent states of nonliving self-propelled particles. We realize an experimental system with dense suspensions of asymmetrical colloidal particles (Janus particles) self-propelling on a two-dimensional surface under an ac electric field. Velocity fields of the Janus particles in the crowded situation can be regarded as a sort of turbulence because it contains many vortices and their velocities change abruptly. Correlation functions of their velocity field reveal the coexistence of polar alignment and antiparallel alignment interactions, which is considered to trigger mesoscopic turbulence. Probability distributions of local order parameters for polar and nematic orders indicate the formation of local clusters with particles moving in the same direction. A broad peak in the energy spectrum of the velocity field appears at the spatial scales where the polar alignment and the cluster formation are observed. Energy is injected at the particle scale and conserved quantities such as energy could be cascading toward the larger clusters.