Abstract
Magnetite/copolymer (Fe3O4/copolymer) composites with nano-size were fabricated by chemical oxidative polymerizaiton and adopted as an additional ingredient in micro-sized carbonyl iron particle (CIP) based magnetorheological fluid (MRF) to improve its dispersion state and rheological performance. Morphologies and magnetic properties of magnetic particles including the composite and CIP were observed by high-resolution scanning electron microscopy and vibrating sample magnetometer. Two types of CIP-based MRFs, with (Bidisperse-MRF) and without (Monodisperse-MRF) magnetite/copolymer composites additive, were prepared using silicone oil as a medium. Rheological performances of Monodisperse-MRF and Bidisperse-MRF were investigated by the steady shear test and oscillatory dynamic test under gradient magnetic field. Flow curves were found to fit the Hershel-Bulkley model well, and the dynamic yield stress and static yield stress were confirmed to follow a universal scaling equation. The sedimentation stabilities of two MRFs were further confirmed using an optical analyzer of Turbiscan. The results shown that the Bidisperse-MRF exhibited improved rheological performance and sedimentation stability, which is attributed to the Fe3O4/copolymer composites filling the free space among the CIPs, thereby inducing stiffer chain structures and a more stable dispersion state.
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