title: Droplets in Microchannels: Dynamical Properties of the Lubrication Film.
abstract: We study the motion of droplets in a confined, micrometric geometry, by focusing on the lubrication film between a droplet and a wall. When capillary forces dominate, the lubrication film thickness evolves nonlinearly with the capillary number due to the viscous dissipation between the meniscus and the wall. However, this film may become thin enough (tens of nanometers) that intermolecular forces come into play and affect classical scalings. Our experiments yield highly resolved topographies of the shape of the interface and allow us to bring new insights into droplet dynamics in microfluidics. We report the novel characterization of two dynamical regimes as the capillary number increases: (i) at low capillary numbers, the film thickness is constant and set by the disjoining pressure, while (ii) above a critical capillary number, the interface behavior is well described by a viscous scenario. At a high surfactant concentration, structural effects lead to the formation of patterns on the interface, which can be used to trace the interface velocity, that yield direct confirmation of the boundary condition in the viscous regime.
authors: MMN, UMR CNRS Gulliver 7083, PSL research University, ESPCI ParisTech, 10 rue Vauquelin, F-75005 Paris, France.
authors: Axel
authors: A
authors: Huerre
authors: Laboratory Adhesion & Inflammation, Aix Marseille Université UM 61; Inserm UMR_S 1067; CNRS UMR 7333; Assistance Publique Hôpitaux de Marseille, 163 avenue de Luminy, 13009 Marseille, France.
authors: Olivier
authors: O
authors: Theodoly
authors: Department of Chemical Engineering, Technion-IIT, Haifa 32000, Israel.
authors: Alexander M
authors: AM
authors: Leshansky
authors: Laboratory Adhesion & Inflammation, Aix Marseille Université UM 61; Inserm UMR_S 1067; CNRS UMR 7333; Assistance Publique Hôpitaux de Marseille, 163 avenue de Luminy, 13009 Marseille, France.
authors: Marie-Pierre
authors: MP
authors: Valignat
authors: IPR, UMR CNRS 6251, Universite de Rennes 1, 35000 Rennes, France.
authors: Isabelle
authors: I
authors: Cantat
authors: MMN, UMR CNRS Gulliver 7083, PSL research University, ESPCI ParisTech, 10 rue Vauquelin, F-75005 Paris, France.
authors: Marie-Caroline
authors: MC
authors: Jullien
mesh_terms: D008153:Lubrication; D044085:Microfluidics; D008962:Models, Theoretical; D013500:Surface Tension; D014783:Viscosity