Statut  Confirmé 
Série  COLLOQUIUMENS 
Domaines  physics 
Date  Mardi 18 Fevrier 2020 
Heure  17:15 
Institut  DPTPHYSENS 
Salle  Amphi Jaurès  Département de Physique de l'ENS 24 rue Lhomond 75005 PARIS 
Nom de l'orateur  Restagno 
Prenom de l'orateur  Frédéric 
Addresse email de l'orateur  
Institution de l'orateur  Laboratoire de Physique des Solides, CNRS, Université ParisSaclay 
Titre  Slip of polymer fluids 
Résumé  Modeling fluid flows in channels is a general problem in science and engineering. For ideal liquids, the situation is simple: there is no dissipation due to fluid movement. For real liquids, some energy is lost. Navier, in his pioneering work on fluid mechanics identified two possible sources of dissipation: bulk dissipation, associated to the viscosity and the friction of the last layer of liquid molecules sliding on the solid surface. For surface dissipation, a classical assumption of fluid dynamics is that a liquid element adjacent to the surface is equal to the velocity of the surface, i.e. a nonslip boundary condition, which leads to no surface dissipation. This is not the only possibility. Navier, postulating the existence of a slip velocity at the surface, introduced the possibility of surface dissipation. He proposed a linear relation between the shear stress at the solidliquid interface and the slip velocity: σ=kV, where k is the interfacial friction coefficient. Indeed, it is also possible to define the slip length b as the distance from the solid surface where the fluid velocity profile extrapolates linearly to zero. During this presentation, I will briefly review what we know on the boundary condition for simple Newtonian liquids and show that polymers, due to their entanglements present a unique tool to study and understand the Navier condition. Based on a setup using the photobleaching of fluorescent polymers, I will present our last results on the slip of polymer melts and polymer solutions. 
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