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 anisotropic 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. [S0031-9007(98)08119-8].