"Matière et Systèmes Complexes"
Lundi 15 juin 2009 à 11h30
Bâtiment Condorcet, 4ème étage, salle 454 A.
Some « visco-elastic» problems
We will in this seminar treat
two systems that deal with the interplay between viscosity and elasticity.
We first present pattern formation during tensile deformation of confined visco-elastic layers. The use of a model system (PDMS with different degrees of crosslinking) allows us to go continuously from a viscous liquid to an elastic solid. We observe two distinct regimes of fingering instabilities: a regime called ''elastic`` with interfacial crack propagation where the fingering wavelength only scales with the film thickness and a bulk regime called “viscoelastic” where the fingering instability shows a Saffman-Taylor-like behavior. We find good quantitative agreement with theory in both cases and present a reduced parameter describing the transition between the two regimes and allowing to predict the observed patterns over the whole range of visco-elastic properties.
We then present the interaction of a flexible elastic fiber with a viscous flow. When the viscous forces acting on the fiber overcome the elastic forces a buckling instability occurs. The subsequent deformation of the elastic fibre then modifies the transport of the latter through a viscous flow. We study this behavior in a cellular flow.