Hollow Structured Magnetic Particles of CoFe2O4 and Their Magnetorheological Characteristics

The hollow structured magnetic CoFe₂O₄ nanoparticles were synthesized by a facile hydrothermal method, and their magnetorheological (MR) characteristics were investigated in this paper. From transmission electron microscopy and density measurements, it was found that the CoFe₂O₄ nanoparticles possess a spherical shape with a narrow size distribution with a low density of 4.46 g/cm³. The MR fluid was then prepared by dispersing CoFe₂O₄ nanoparticles in mineral oil. Under applied magnetic fields, its rheological properties, such as shear stress, shear viscosity, storage modulus, and yield stress, were investigated via a rotational rheometer with a parallel-plate geometry. In addition, suspension stability of the CoFe₂O₄-based MR fluid was also examined by a Turbiscan apparatus, demonstrating that the CoFe₂O₄ suspension has good dispersion stability due to the unique hollow architecture and the relatively low density.