Active versus Passive Hard Disks against a Membrane: Mechanical Pressure and Instability
Résumé
We experimentally study the mechanical pressure exerted by a set of respectively passive isotropic and
self-propelled polar disks onto two different flexible unidimensional membranes. In the case of the isotropic
disks, the mechanical pressure, inferred from the shape of themembrane, is identical for both membranes and
follows the equilibrium equation of state for hard disks. On the contrary, for the self-propelled disks, the
mechanical pressure strongly depends on the membrane in use and thus is not a state variable. When selfpropelled
disks are present on both sides of the membrane, we observe an instability of the membrane akin to
the one predicted theoretically for active Brownian particles against a soft wall. In that case, the integrated
mechanical pressure difference across the membrane cannot be computed from the sole knowledge of the
packing fractions on both sides, further evidence of the absence of an equation of state.
Domaines
Matière Molle [cond-mat.soft]
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