Collective motion in a sheet of microswimmers

Dóra Bárdfalvy, Viktor Škultéty, Cesare Nardini, Alexander Morozov, Joakim Stenhammar*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

Self-propelled particles such as bacteria or algae swimming through a fluid are non-equilibrium systems where particle motility breaks microscopic detailed balance, often resulting in large-scale collective motion. Previous theoretical work has identified long-ranged hydrodynamic interactions as the driver of collective motion in unbounded suspensions of rear-actuated (“pusher”) microswimmers. In contrast, most experimental studies of collective motion in microswimmer suspensions have been carried out in restricted geometries 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 between two no-slip walls. For pushers, we demonstrate collective motion with short-ranged order, in contrast with the long-ranged flows observed in unbounded systems. For front-actuated (“puller”) microswimmers, we discover a long-wavelength density instability resulting in the formation of dense microswimmer clusters. Both types of collective motion are fundamentally different from their previously studied counterparts in unbounded domains. Our results show that this difference is dictated by the geometrical restriction of the swimmers’ motion, while hydrodynamic screening due to the presence of a wall is subdominant in determining the suspension’s collective state.
Original languageEnglish
Article number93
Pages (from-to)1-8
Number of pages8
JournalCommunications Physics
Publication statusPublished - 14 Mar 2024

Keywords / Materials (for Non-textual outputs)

  • cond-mat.soft
  • cond-mat.stat-mech
  • physics.flu-dyn


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