Collective trapping of flocking particles by asymmetric obstacles*

Anisotropic obstacles not only are capable to induce ratchet effects on suspensions of run-and-tumbling particles, but also affect the collective behaviour of active aligning particles, such as Vicsek particles [1, 2]. In this talk, I will show that flocking particles which follow the Vicsek model aligning rules experience a collective trapping in the presence of a wall of funnels made of chevrons, concentrating at the opposite side of a wall of funnels than run-and-tumbling particles. We study the dynamics of this collective self-trapping behaviour and identify two regimes, one static and other dynamical in which particles are effectively trapped by constantly escaping and getting into the channels. Exploiting these two regimes, we engineer a system showing two perpendicular flows of Vicsek particles.

[1] T. Vicsek, A. Czirok, E. Ben-Jacob, I. Cohen, and O. Shochet, Physical review letters 75, 1226 (1995).
[2] J. A. Drocco, C. O. Reichhardt, and C. Reichhardt, Physical Review E 85, 056102 (2012).