From Wall-Climbing Active Colloids to self-assembly of Magnetotactic Bacteria

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• Prof Cottin-Bizonne, Université Lyon
• Friday 23 May 2025, 16:00-17:00
• MR2.

If you have a question about this talk, please contact Professor Grae Worster.

The observation of flocks of birds, schools of fish, and swarms of bees reveals captivating examples of collective behavior in nature. Over the past decade, physicists have unveiled intriguing features in such systems, giving rise to both spectacular phenomena and fundamental questions. In this presentation, we will first explore active wetting phenomena in a suspension of self-propelled Janus colloids near a vertical wall. While classical capillary rise is governed by equilibrium surface tension, active fluids challenge this paradigm. We investigate whether analogous interfacial effects emerge in non-phase-separated active sediments, uncovering how self-propulsion modifies wetting behavior. By studying the interaction between a non-phase-separated active sediment and a wall, we uncover how self-propulsion alters wetting-like behavior, offering insights into the role of activity in interfacial processes. In the second part, we turn to magnetotactic bacteria— microswimmers equipped with intracellular magnetic nanoparticles, enabling directed motion along magnetic fields. These bacteria exhibit dual sensitivity, responding not only to magnetic fields (magnetotaxis) but also to oxygen gradients (aerotaxis), which drives them to form dense, dynamic bands. We demonstrate how the interplay of magnetic steering, chemical gradients, and hydrodynamic interactions leads to rich self-organization.

This talk is part of the Fluid Mechanics (DAMTP) series.

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