Abstract
We analyze the experimental data on the motion of active Brownian micrograins in RF discharge plasmas. In the experiments, two types of microparticles were used: first—plastic grains fully covered with metal, and second—Janus particles with a thin metal cap. We have tracked the trajectories of the separate grains and plotted the pair correlation functions of the observed structures. To examine the motion of the grains, we studied the dependencies of the MFPT dynamic entropy on the coarsening parameter, the fractal dimension of the system on its mean kinetic temperature, and the mean localization area of the grain on its mean kinetic temperature. Based on the obtained results, we conclude that the character of motion of our active Brownian systems changes as the power of an illuminating laser (and, therefore, the mean kinetic temperature of the grains) increases. Janus particles change their trajectories from more chaotic to spiral-like ones; in the case of fully covered particles, we observe the dynamical phase transition from the more ordered structure to the less ordered one.
Highlights
In the last ten years, the problems considering the dynamics of so-called active Brownian, or self-propelled, particles, have become more and more essential
We study the underdamped motion of two kinds of active Brownian particles in plasma: laser-activated grains and Janus particles
We have analyzed the experimental data on the motion of active Brownian micrograins in RF-discharge plasmas
Summary
In the last ten years, the problems considering the dynamics of so-called active Brownian, or self-propelled, particles, have become more and more essential. These particles possess the unique property to convert external energy into the kinetic energy of their motion [1–3]. The nature of these particles may be various: colloid grains in buffer media [4,5], protozoa and bacteria [6,7], chemically activated particles [8–10] and, even, mechanical objects [11–14]. For example, one can observe dynamical phase transitions and phase separation in the structures of active Brownian particles that have no analogues in the passive Brownian systems [17,18]. One of the remarkable examples of such an outstanding difference is the motility-induced phase separation (MIPS), which is often observed in the systems of self-propelled particles [2,19,20]
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