Conductive Properties Of Magnetorheological Elastomers

Magnetorheological elastomers(MREs) are elastic solids composed of micron sized soft magnetic particles and polymer matrix. The particles are dispersed into the liquid precursors of polymers, and then the suspension is exposed to a magnetic field until the vulcanization is finished. The particles form ordered structures in MREs because magnetorheological effect occurs in the suspension. The form of long chains can be used as a conducting channel to make the MREs have electrical conductivity. Compared with the conventional conductive polymer composites,MREs have many advantages such as low resistance,simple preparation and multi parameters. There is a high practical value.The preparation process of MREs and the particle structure of MREs were analyzed, and the factors which affect the electrical conductivity of MREs were studied, such as the external pressure, working magnetic field, temperature and so on.The basic preparation process was finalized by analyzing the requirements for materials. Carbonyl iron powders and silicon rubber were used as the basic materials for MREs preparation. The particle structure was observed experimentally and the effect of the strength of magnetic field and the volume fraction of particles was analyzed.The conductive mechanism of MREs was analyzed with consideration of the effects of particle structure, and the conductivity model of MREs was derived by analyzing the tunneling current and conduction current inside MREs. Conduction current played an important role when the electric field intensity was small. The tunneling current played an important role in the electric field intensity. Due to the tunneling current, there was a nonlinear relationship between the conductivity and the electric field strength of MREs. Based on the Hertz contact theory and the conduction mechanism model of MREs, the theoretical model of pressure-sensitive property was derived. The electrical conductivity and pressure sensitivity of MREs were analyzed, and the experimental results agreed with the theoretical predictions very well.The effect of applied magnetic field on the conductivity of MREs was studied.The interaction force of adjacent particles was analyzed by the dipole model of magnetized particles. The magnetic field-effect of MREs was affected by analyzing the area of conductive path. The experimental results of the relationship between the resistivity and magnetic induction intensity of MREs showed that the resistivity of MREs decreases with the increase of magnetic field strength. When the magnetic field strength increases, the resistivity decreases gradually, and finally reaches a steady state.Due to the thermal conductivity of the conductive filler and the matrix material is different. The electrical conductivity of MREs was affected by the interparticle gap dependent on the temperature. It was also derived by analyzing the effect of temperature on the conductivity of MREs, which is induced by the conductive mechanism of MREs. The temperature characteristics of MREs were studied. It was found that MREs showed obvious temperature effect, and the conductivity of MREs decreased with increasing temperature.