The mesoscopic clustering behavior of sub-propulsive active particle suspension confined in micro-channel

Chong-Wai Io^1*, Yu-YaoLee¹

¹Dept. of Phys., National Chung-Cheng University, Chia-Yi, Taiwan

* Presenter:Chong-Wai Io, email:phycwio@ccu.edu.tw

The suspension of active particles with tunable self-propulsion strength could be one of the simplest non-equilibrium systems. With increasing the self-propulsion strength, such a system can bridge the equilibrium state with Brownian motion to far from equilibrium state with heterogeneous structures and motions, even the background is homogeneous (without any consideration of boundary effect). The spatial confinement is an additional factor driving the system away from equilibrium, which also makes the background inhomogeneous. The studies of spatial confinement have been a hot topic in the past decade. Nevertheless, most of the previous studies mainly focused on the propulsion-dominated regime. How the sub-propulsive strength cooperating with spatial confinement to exhibits interesting behaviors has rarely been discussed, which is fatally important for the low mobility bacterium suspension. In this work, by confining the thermophoretic type active particle suspension into a high aspect ratio microchannel and operating at the sub-propulsive regime, many interesting clustering behaviors are experimentally explored, such as the sausage-like bundle, quasi-periodic isolated cluster, and a-periodic isolated cluster, and typical boundary accumulation. The corresponding formation mechanism is also discussed.

Reference: PRE 104, 014607 (2021)

Keywords: microchannel, active particle, mesoscopic clustering