Collective motion in a sheet of microswimmers
D\'ora B\'ardfalvy, Viktor \v{S}kult\'ety, Cesare Nardini, Alexander, Morozov, and Joakim Stenhammar

TL;DR
This study uses numerical simulations to explore how microswimmers behave collectively in a confined, quasi-2D environment, revealing that boundaries significantly alter their collective motion compared to unbounded systems.
Contribution
The paper introduces a minimal model for microswimmers in confined geometries, showing that boundary effects dominate the nature of collective motion, differing from unbounded suspension behaviors.
Findings
Pushers exhibit short-range collective order in confined geometry.
Pullers develop long-wavelength density instabilities leading to clustering.
Hydrodynamic screening by walls is less influential than geometric restrictions.
Abstract
Self-propelled micron-size particles suspended in a fluid, like bacteria or synthetic microswimmers, are strongly non-equilibrium systems where particle motility breaks the microscopic detailed balance, often resulting in large-scale collective motion. Previous theoretical work has identified long-range hydrodynamic interactions as the main driver of collective motion in unbounded dilute suspension of rear-actuated ("pusher") microswimmers. In contrast, most experimental studies of collective motion in microswimmer suspensions have been carried out in quasi-2-dimensional geometries such as in thin films or near solid or fluid interfaces, where both the swimmers' motion and their long-range flow fields become altered due to the proximity of a boundary. Here, we study numerically a minimal model of microswimmers in such a restricted geometry, where the particles move in the midplane…
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Taxonomy
TopicsMicro and Nano Robotics · Microfluidic and Bio-sensing Technologies · Orbital Angular Momentum in Optics
