Shear Banded Flows and Nematic-to-Isotropic Transition in ER and MR Fluids

Above a critical shear rate we observe in suspensions polarized by an external field an abrupt jump of stress and the onset of a layered stripe pattern. This novel shear-induced transition can be systematically found by using appropriated geometry. We show that it can be explained by the transition from a nematiclike order induced by the field to an isotropic state which is obtained when the shearing hydrodynamic forces on a pair of particles overcome the magnetic or electrostatic forces. The critical shear stress predicted on this basis is in good agreement with the experimental results.