Putting stubborn flocks to work

Building on spontaneously flowing liquids assembled form colloidal rollers, I will show that (french) active colloids collectively protest and resist when one tries to waive their privilege to freely choose their direction of motion. I will show that the flows emerging from flocking transitions are intrinsically bistable and can proceed against external pressure gradients. I will theoretically explain this collective stubbornness showing that orientational elasticity and confinement conspire to protect the direction of spontaneous flows. Finally, I will show how to exploit the intrinsic bistability of confined polar liquids introducing a generic design principle for self-sustained microfludiic oscillators.