Hybrid magnetic particles of carbonyl iron (CI)/poly(vinyl butyral) (PVB) with core/shell microstructure (CI-PVB) were prepared in order to enhance the dispersion stability of the magnetorheological (MR) fluids. Since the composite particles of CI-PVB have a lower density than that of the pristine CI particles, they are regarded to improve the sedimentation problem of magnetic particles in the MR fluid when the particles are dispersed in a mineral oil and to make easy redispersion after caking. The PVB coating layers were found to play an important role in the steric repulsion between the relatively large CI particles. Morphology and composition of the CI-PVB particles were observed via SEM and TGA, respectively. Flow properties of both CI and CI-PVB based MR fluids were examined via a rotational rheometer in parallel plate geometry equipped with a magnetic field supplier.
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