Lateral migration and segregation of vesicles with viscosity contrast in simple shear and Poiseuille flows
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1132-Z02-09
Lateral migration and segregation of vesicles with viscosity contrast in simple shear and Poiseuille flows Gwennou Coupier1, Natacha Callens2, Badr Kaoui1,3, Christophe Minetti2, Frank Dubois2, Chaouqi Misbah1 and Thomas Podgorski1 1
Laboratoire de Spectrométrie Physique, Université Joseph Fourier (Grenoble I) and CNRS, 140 Rue de la Physique, F-38402 St Martin d'Hères Cedex, France 2 Microgravity Research Center, Université Libre de Bruxelles, 50 Av. F. Roosevelt, CP 165/62, B-1050 Brussels, Belgium 3 Université Hassan II - Mohammedia, Faculté des Sciences Ben M'Sik, Laboratoire de Physique de la Matière Condensée, BP 7955 Casablanca, Morocco ABSTRACT Lateral migration of vesicles (closed lipidic membranes) in a flow is characterized as a function of the relevant flow parameters and mechanical properties of the vesicles. We consider low Reynolds number flows, and migration is only due to viscous effects. Through experiments and simulations, we exhibit two different origins for such cross streamline migration: the presence of a wall, and a non-constant shear rate, as for instance in a Poiseuille flow. Such migration modifies the distribution of vesicles in a sheared polydisperse suspension; we present preliminary results proving that the hydrodynamic interactions between vesicles greatly modify the distribution of vesicles according to their sizes and deflation. INTRODUCTION The ability of soft entities such as vesicles, drops, capsules or blood cells, to adapt their shapes under non-equilibrium conditions gives them the possibility to migrate transversally to the streamlines even at low Reynolds number. Those transverse migrations induce non-uniform lateral distributions of the suspended objects, which has important consequences on the rheology of a confined suspension, as illustrated for instance the Fahraeus-Lindquist effect in blood vessels [1]. Vesicles are closed phospholipid membranes; they encapsulate an internal fluid and are usually suspended in an external aqueous solution. The physics of vesicles has attracted much interest in the recent decades and have been the subject of many theoretical and experimental works. This is because of their ability to reproduce some dynamical behaviors observed for living cells (such as red blood cells [2]) and the interest to exploit them as carriers of biomaterials. Vesicle dynamics in shear flow has been the subject of extensive studies [3-9]. A vesicle placed in an unbounded fluid subject to simple shear does not exhibit any lateral migration with respect to the flow direction. When the viscosity ratio between the inner and the outer fluids is small, it performs a tank-treading dynamics where the orientation of the main axis of the vesicle is constant and the membrane undergoes a tank-treading motion. We shall see in the following that once this flow is bounded by a wall and/or the velocity profile is not linear (non homogeneous shear rate), tank-treading vesicles experiment transverse forces inducing lateral migration, even in the Stokes limit, when iner
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