Adaptive magnetorheological materials

In this paper we review some recent results we have obtained with composite materials made of micron-sized magnetic particles dispersed either in a liquid (Magnetorheological fluids) or in an elastomer (Magnetorheological elastomers). In the case of MR fluids we derive the flow profile in a capillary in the presence of a magnetic field and extend this result to the case of a MR fluid pushed through a porous medium. We find that, in such a situation, a strong modulation of the pressure can be obtained even with a quite low magnetic field. Another related situation, where a flow blockage is obtained by approaching a magnet to a ferrofluid containing non magnetic particles, is also described, having in mind applications for thrombosis around tumoral cells. In the case of MR elastomers we show how a large change of elasticity can be obtained by the application of a magnetic field both under steady and oscillatory strain. We relate this behaviour to the organization of the filler particles and also find that such an elastomer can show a large magnetostrictive effect.