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Nage de suspensions actives en milieu complexe

Abstract : The active suspensions are defined as assemblies of self-propelled particles in a fluid. They are composed of a variety of different systems such as bacteria, micro-robots, or planktons. These active systems inspire several scientific communities (Physics, Mechanics, Biology and Mathematics) in order to develop a universal understanding to describe this new state of matter. Providing their own energy for moving in bulk, these systems are often considered as interesting models to answer the questions related to non-equilibrium statistical physics. This thesis aims at understanding the interactions between the motion of particles and its complex environment. The micro-swimmer Chlamydomonas Reinhardtii (CR), chosen as a model of active particles, is studied with several complementary approaches incorporating experiments, theory and numerical simulations. The use of soft lithography as the micro-fabrication technique allows us to create various complex environments made of confinements and networks of micro-pillars. Those environments can disturb the hydrodynamic fields generated by the micro-swimmers. Thus, the presence of obstacles and confinements affects the dynamics of the particles, resulting from steric hindrances coupled with long-range hydrodynamic interactions. In this case, the CR has an evolving diffusivity with confinement, which can be explained by geometric and hydrodynamic arguments. Additionally, phototaxis (repulsion of micro-swimmers by a light source) in a complex medium is also studied. The swimming of the CRs then become entirely ballistic, so that we can study the suspensions’ motion through a constriction. Particularly, clogging and faster-is-slower effects are observed in the micro-swimmers, as well as in many other systems (pedestrians, sheeps, mice, numerical simulations, etc...) revealing the significant role of friction between cells.
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  • HAL Id : tel-02501274, version 1

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Marvin Brun-Cosme-Bruny. Nage de suspensions actives en milieu complexe. Biophysique [physics.bio-ph]. Université Grenoble Alpes, 2019. Français. ⟨NNT : 2019GREAY045⟩. ⟨tel-02501274⟩

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