Pantheon SEMPARIS Le serveur des séminaires parisiens Paris

Status Confirmed
Seminar Series COLLOQUIUM-ENS
Subjects physics
Date Tuesday 18 February 2020
Time 17:15
Institute DPT-PHYS-ENS
Seminar Room Amphi Jaurès - Département de Physique de l'ENS 24 rue Lhomond 75005 PARIS
Speaker's Last Name Restagno
Speaker's First Name Frédéric
Speaker's Email Address
Speaker's Institution Laboratoire de Physique des Solides, CNRS, Université Paris-Saclay
Title Slip of polymer fluids
Abstract 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 non-slip 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 solid-liquid 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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