Zigzag pattern of active shakers
Today we had a guest seminar by Gaspard Junot (LOMA, University of Bordeaux). He seems to have been a colleague of Kato-san during her stay in France. The talk was based on the PRL paper shown below [1].
![The paper [1] presented by Gaspard Junot.](/blog/2606031/Junot2023.png)
The study showed that when active shakers are suspended in a viscoelastic fluid, hydrodynamic interactions between the shakers lead to the emergence of large-scale zigzag patterns. The zigzag angle can be explained by the flow field generated by the active shakers themselves, and the overall structure of the talk was exceptionally well organized and engaging. Starting from an experimentally accessible system, revealing a surprising macroscopic phenomenon, and then explaining its underlying mechanism—it was a very elegant story. I learned a lot from it.
The induced flow field resembled the one that appears in the well-known squirmer model. So I jokingly asked Changle, a member of our lab, "Do Chlamydomonas (microalgae) also form zigzag patterns?" To my surprise, the answer was yes. When strong LED lights are applied from both sides, negative phototaxis causes the cells to align into a band-like structure, which subsequently becomes unstable and develops into a zigzag pattern through hydrodynamic instability. Fascinating.
![The active-jet paper on Chlamydomonas [2] that Changle told me about. It seems that [Ishikawa Lab](https://www.bfsl.mech.tohoku.ac.jp/) at Tohoku University was involved in the work.](/blog/2606031/Eisenmann2025.png)
References
[1] I. Eisenmann, M. Vona, N. Desprat, T. Ishikawa, E. Lauga and R. Jeanneret, “Pure Hydrodynamic Instabilities in Active Jets of Puller Microalgae”, Phys. Rev. Lett. 135, 198301 (2025). https://link.aps.org/doi/10.1103/jjcv-ygvq
[2] G. Junot, M. De Corato and P. Tierno, “Large Scale Zigzag Pattern Emerging from Circulating Active Shakers”, Phys. Rev. Lett. 131, 068301 (2023). https://link.aps.org/doi/10.1103/PhysRevLett.131.068301