Flow at micro and nanoscale

Orateur : Oriane BONHOMME (Laboratoire de Physique de la Matière Condensée et Nanostructures, LPMCN)

The first part of my talk deals with fundamental studies on flow and transport phenomena that lead to functional fiber formation in microfluidics. First, we study coflows of miscible fluids, configuration used for shaping up the fiber. We prove that the use of complex fluids brings some limitations (hydrodynamic instability or dynamically-created heterogeneities) on the control of the jet shape. I will present results on the flow of dense suspension of non-Brownian hard spheres. I will then explain how fibers can be fabricated in a microfluidic chip by gelation of alginate with a calcium salt. We investigate the influence of control parameters on the gelation process and the kind of structure created (no gel, fiber, pieces-of-gel and clogging). To describe the resulting state diagrams, we develop a model of reaction ?diffusion under flow and identify the gel strength and the stress exerted on the jet as control parameters. To finish, I will present the high-concentrated cell laden fibers that we finally manage to create. These structures are really promising for tissue-engineering application. The second part of my talk concerns flow at nanoscale. I will show you original results on electroosmotic flow in soap films (easy-to-made and easily tunable nanofluidic systems). In contrast to systems confined between solid surfaces, the soft nature of the nanochannel results in a thickening of the film. This effect increases with the applied electric field. We develop a model, in analogy with a Landau-Levich film withdrawn from a reservoir, to rationalize these observations. Paradoxically, the flow velocity does not seem to be influenced by the surface deformability.

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