INFLUENCE OF MICROSTRUCTURAL ANISOTROPY ON THE MAGNETORHEOLOGICAL EFFECT IN ELASTOMER-BASED COMPOSITES WITH IRON PARTICLES

The results presented in this paper are a part of the studies on development of magnetorheological elastomers based on ferromagnetic particles in a polyurethane matrix. The influence of the amount of the ferromagnetic particles and their arrangement in relation to the external magnetic field was investigated. Scanning electron microscopy was used to observe MRE microstructure. The particles orientation and their arrangement were also investigated with vibrating sample magnetometer (VSM). Rheological properties of obtained MREs were studied with and without application of an external magnetic field. It was found that the microstructure of the MRE depends on the amount of ferrous particles. The orientation of the iron particles into aligned chains is possible for a lower volume content of ferromagnetic filler. Magnetic measurements confirmed the existence of microstructure anisotropy for MREs with 1.5; 11.5; 18 and 25 vol. % of iron particles. This structural and magnetic anisotropy has not been found in the the MRE with 33 vol. % of carbonyl-iron. Both the particles content and their chains direction have significant effect on the rheological properties of magnetorheological urethane elastomers. Application of an external magnetic field leads to a significant increase in elastic modulus. Relative changes of storage modulus, calculated from obtained curves, show that the samples microstructure has a significant effect on their magnetorheological effect.