Performance of isotropic magnetorheological rubber materials

Magnetorheological (MR) rubber materials are the solid analog of magnetorheological fluids; hence, their rheological properties can be controlled by an applied magnetic field. If the particles embedded in the matrix are carbonyl iron, they have to be aligned by a magnetic field before the curing of the rubber, in order to achieve a substantial MR effect. However, the use of a crosslinked matrix allows larger particles to be used. We show that MR rubber materials with large irregular particles have a large MR effect although the particles are not aligned within the material. This is explained by the low critical particle volume concentration of such particles. A similar effect can be obtained for materials with carbonyl iron, if the particles are badly dispersed and thereby behaving like larger irregular particles. Besides the achieved level of dispersion, the rheological properties of the matrix material do not influence the MR effect.