Enhancement of the magnetorheological effect using discontinuous shear thickening with a mixture of magnetic and non magnetic particles

The phenomenon of discontinuous shear thickening (DST) is observed in suspensions of solid particles with a very high-volume fraction. Using a suspension of magnetic particles at high-volume fraction we have, for the first time, demonstrated experimentally the presence of a frictional network of particles by a simultaneous measurement of the electrical resistance of the suspension and of the rheological curve. An obstacle for the applications of MRS remains the sedimentation and aggregation linked to the high density of the iron microparticles. We have recently found that a small fraction of ferromagnetic particles within a concentrated suspension of calcium carbonate particles is not only sufficient to trigger the transition by application of a magnetic field but also optimum for the amplitude of the jump in viscosity observed in DST. We shall explain this result from stress transmission between the magnetic particles and nonmagnetic ones, both inserted in the percolated network of particles. We will also highlight the role of the polyelectrolyte adsorbed on the surface of the particles in the DST transition through the balance between the repulsive entropic force between two layers of polymer adsorbed on different particles and the magnetic attraction force.