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Du mouvement au blocage collectif dans des assemblées de rouleurs colloïdaux : hydrodynamique et solidification des liquides polaires actifs

Abstract : Spontaneous collective motion arises in many different systems, from assembly of synthetic shaken grains to living bird flocks. In order to understand the generic features of those collective behaviours, physisicts describe the flocks of motile units as ordered materials. In this thesis we study experimentally the dynamics of synthetic flocks and explore their hydrodynamic properties. We take advantage of the Quincke mechanism to motorize millions of colloids. Those Quincke rollers self-organize into a polar liquid, where all the particles, on average flow in the same direction. We provide the first experimental proof that the dynamics of polar liquids is well described by a theoretical prediction established more than twenty-five years ago. In particular, we demonstrate that two sound modes propagate along all directions of the fluid and we design a non invasive spectroscopic method to measure its hydrodynamics constants.Finally, we show that collective motion can be arrested in a dense flock. An active solid can nucleate, grow and propagate in a polar liquid. We establish that this solidification is a first order phase transition and demonstrate that the formation of this active solid is the first experimental proof of a complete motility induced phase separation of active particles (also known as MIPS).
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https://tel.archives-ouvertes.fr/tel-02383177
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Submitted on : Wednesday, November 27, 2019 - 3:46:34 PM
Last modification on : Thursday, March 5, 2020 - 3:26:49 PM

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  • HAL Id : tel-02383177, version 1

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Delphine Geyer. Du mouvement au blocage collectif dans des assemblées de rouleurs colloïdaux : hydrodynamique et solidification des liquides polaires actifs. Matière Condensée [cond-mat]. Université de Lyon, 2019. Français. ⟨NNT : 2019LYSEN026⟩. ⟨tel-02383177⟩

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