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Abstract: Soft‐magnetic polystyrene (PS)/Fe3O4 core/shell composite nanoparticles are fabricated by surfactant‐free Pickering emulsion polymerization using Fe3O4 nanoparticles as a solid stabilizer. The morphology of the synthesized PS/Fe3O4 particles consisting of a PS surface coated with Fe3O4 nanoparticles is examined by scanning electron microscopy and transmission electron microscopy. The thermal properties of Fe3O4 and PS/Fe3O4 are examined by thermogravimetric analysis, while the chemical bonding and composition of the nanocomposite are characterized by Fourier transform infrared spectroscopy and X‐ray diffraction. The magnetorheological (MR) properties of the PS/Fe3O4 composite nanoparticles dispersed in silicone oil are analyzed using a rotational rheometer under an external magnetic field. The PS/Fe3O4‐based MR fluids exhibit typical MR properties and a lower density compared to Fe3O4 nanoparticles, indicating the improved dispersion stability of the MR fluid compared to that of the Fe3O4 nanoparticle‐based MR fluid. [ABSTRACT FROM AUTHOR]

Magnetic Fe3O4@SiO2 nanoparticles were initially synthesized by a sol-gel process and introduced to a soft magnetic carbonyl iron particle-based magnetorheological (MR) fluid to improve its MR properties and dispersion stability. Structure and properties of the core–shell Fe3O4@SiO2 nanoparticles were characterized, showing that they are soft magnetic. MR characteristics of two MR fluid systems with and without Fe3O4@SiO2 additives were investigated and compared under different magnetic field strengths using a rotational rheometer, exhibiting typical MR behaviors. Dispersion stability of the MR fluid was also characterized by an optical analyzer system of Turbiscan. [ABSTRACT FROM AUTHOR]