UMR 5672

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Micro-swimmers in confinement: hydrodynamics and spatially-dependent enhanced colloidal diffusion

Raphaël Jeanneret (IMEDEA, Spain)
When Nov 05, 2019
from 10:45 AM to 11:45 AM
Where Room André Collet (M6)
Attendees Raphaël Jeanneret
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Geometrical confinement strongly affects the hydrodynamic interactions (HI) between particles, whether those are passive and externally driven or self-propelled. For instance passive droplets cruising in Hele-Shaw channels interact via long-range dipolar HI due to a mismatch between fluid and particles velocity (originating from lubricated friction with the confining walls). This leads to complex and often counter-intuitive collective phenomena such as dispersive density waves propagation and shock waves. Confinement is also often considered in theoretical studies exploring the collective behavior of active particles. In such cases HI are usually implemented following predictions which have not yet real experimental supports. With the aim to fill this gap, in this talk I will report on the first systematic measurements of the effect of confinement on the self-generated flow-fields of unicellular flagellated microorganisms taken as model micro-swimmers. Our experimental and theoretical results show that, rather than simplifying further the general pusher/puller bulk classification, confinement enhances the diversity of microbial flow-fields with respect to small morphological differences. In the second part of the seminar (mostly independent of the first one), I will consider an experimental setup where a dilute binary suspension of ~10-um colloids and similarly sized micro-swimmers (Chlamydomonas cells) is confined within quasi-2D microfluidic channels of finite width (i.e. comparable to the persistence length of the swimmers). Because of the interaction of the cells with the lateral walls, in such situation the background active noise provided to the colloids is spatially-dependent. This leads to non-trivial colloidal distributions across the chamber width, which can be studied within a framework of spatially-dependent jump-diffusion processes.