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From pressure to surface tension, the anomalous mechanical properties of active particles
Active particles dissipate energy to exert self-propelling forces on their environment. This microscopic drive out of equilibrium leads to rich behaviors, from the flocking of birds to the motility-induced phase separation of self-propelled colloids or bacteria, that have attracted a lot of attention in the past. This exchange of momentum with the environment also impacts their collective mechanical properties, a topic which has been much less studied. In this talk, I will review recent developments concerning the mechanical pressure and the surface tension of active systems and show how statistics and mechanics decouple in these non-equilibrium systems, leading to surprising properties.
A. P. Solon, Y. Fily, A. Baskaran, M. E. Cates, Y. Kafri, M. Kardar, J. Tailleur, "Pressure is not a state function for generic active fluids", Nature Physics 11, 673-678 (2015)
N. Nikola, A. P. Solon, Y. Kafri, M. Kardar, J. Tailleur, R. Voituriez , "Active particles on curved surfaces : Equation of state, ratchets, and instabilities", Phys. Rev. Lett. 117, 098001 (2016)
R. Zakine, Y. Zhao, M. Knezevic, A. Daerr, Y. Kafri, J. Tailleur, F. van Wijland, "Surface Tensions between Active Fluids and Solid Interfaces : Bare vs Dressed", Physical Review Letters 124, 248003 (2020)