Dario Vincenzi - Universite Cote d Azur, CNRS, LJAD - Keywords: polymer solutions, chaotic dynamics

Dario Vincenzi - Universite Cote d Azur, CNRS, LJAD - Keywords: polymer solutions, chaotic dynamics

Contribution title: Emergence of chaos in a viscous solution of microscopic rods

In a laminar flow the dispersion of substances occurs by molecular diffusion, which operates on extremely long time scales. Various strategies have therefore been developed, particularly in microfluidic applications, to accelerate mixing and dispersion at low fluid inertia. The available strategies are commonly divided into two classes, passive or active, according to whether the desired effect is obtained through the specific geometry of the flow or through an oscillatory forcing within the fluid. An alternative method for improving the mixing properties of low-Reynolds-number flows was proposed by Groisman and Steinberg [Nature, 405, 53 (2000)] and consists in adding elastic polymers to the fluid. If the inertia of the fluid is low but the elasticity of polymers is large enough, elastic stresses give rise to instabilities that ultimately generate a chaotic regime known as "elastic turbulence". In this regime the velocity field, although remaining smooth in space, becomes chaotic and develops a power-law energy spectrum, which enhances the mixing properties of the flow. While the use of elastic turbulence in microfluidics is now well established, new potential applications have recently emerged, namely in oil extraction from porous rocks. We propose a mechanism for generating chaotic flows at low Reynolds numbers that does not rely on elasticity and is based on the addition of rigid rodlike polymers to a Newtonian fluid.