Active versus Passive Hard Disks against a Membrane: Mechanical Pressure and Instability

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 the membrane, is identical f...

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Bibliographic Details
Published in:Physical review letters 2017-07, Vol.119 (2), p.028002-028002, Article 028002
Main Authors: Junot, G, Briand, G, Ledesma-Alonso, R, Dauchot, O
Format: Article
Language:English
Subjects:
Condensed Matter
Physics
Soft Condensed Matter
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Summary: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 the membrane, 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 self-propelled 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.
ISSN:0031-9007
1079-7114
DOI:10.1103/PhysRevLett.119.028002