Magnetorheology of Fiber Suspensions. I. Experimental Authors

SYNOPSIS This work reports a detailed study on the shear magnetorheology of suspensions of magnetic microfibers. The steady-state regime was investigated using a controlled-stress rheometer, for different concentrations of particles and under the presence of a broad range of applied magnetic fields (up to 512 kA m-1). The results were compared with those obtained for conventional magnetorheological fluids (suspensions of magnetic microspheres). It was found that the suspensions of magnetic fibers show an enhanced magnetorheological effect. We proposed the existence of field-dependent solid friction between fibers as the main physical reason for this enhancement. In order to ascertain the relevance of the interfiber solid friction, the microscopic structure of fiber suspensions was investigated using an optical microscope. In the absence of applied field, fibers form an entangled network with approximately isotropic orientation. Upon magnetic field application, the fiber network becomes deformed and 2 approximately aligned with the field direction. Nonetheless, interfiber solid friction hinders a complete alignment of the fibers with the field, and the fiber network remains entangled.