Wave-driven active systems at fluid interfaces
Conf’luence Giuseppe Pucci
National Research Council of Italy (CNR)
Vendredi 10 avril à 10h30 • Amphithéâtre Nougaro
Active systems consist of self-driven units that convert energy from their environment into motion or mechanical forces. Their study has motivated efforts to extend statistical mechanics to nonequilibrium systems. Most work to date has focused on two limiting regimes: overdamped systems, such as bacteria and colloids, whose interactions are mediated by viscous flows that decay monotonically with distance, and inertial systems, such as flocks of birds or schools of fish, characterized by complex spatiotemporal interactions.
In this talk, I will review recent work on wave-driven active systems at vibrating fluid interfaces, which operate in an intermediate regime where both viscosity and inertia play important roles. In these systems, interactions are mediated by surface waves and are therefore spatiotemporally oscillatory, leading to collective behaviors that differ qualitatively from those observed in more conventional active matter.
I will first present hydrodynamic spin lattices, an active system composed of droplets that orbit in submerged wells while interacting through the waves they generate on a vibrating bath [1]. The resulting wave-mediated coupling gives rise to emergent collective states with striking analogies to magnetic ordering in electronic systems.
In the second part of the talk, I will introduce recent work on capillary surfers [2,3] and capillary spinners [4], asymmetric solid particles that propel or rotate at a vibrating fluid interface through asymmetric wave generation. Their propulsion speed and interactions can be tuned through particle geometry, fluid properties, and vibration parameters. Surfers interact through their mutual capillary wavefield and exhibit multiple bound states characterized by discrete equilibrium spacings, while spinners display synchronization phenomena arising from wave-mediated coupling.
These systems provide a tunable platform for exploring active matter with oscillatory long-range interactions at intermediate Reynolds numbers.
[1] Sáenz et al. Nature 596, 58 (2021).
[2] Ho et al. Phys. Rev. Fluids 8, L112001 (2023).
[3] Oza et al. Phys. Rev. Fluids 8, 114001 (2023).
[4] Barotta et al. Phys. Rev. E 111, 035105 (2025).