Emergence of chaos in a viscous solution of rods

It is shown that the addition of small amounts of microscopic rods in a viscous uid at low Reynolds number causes a significant increase of the flow resistance. Numerical simulations of the dynamics of the solution reveal that this phenomenon is associated to a transition from laminar to chaotic ow. Polymer stresses give rise to flow instabilities which, in turn, perturb the alignment of the rods. This coupled dynamics results in the activation of a wide range of scales, which enhancesthe mixing efficiency of viscous flows.