Synthesis and characterization of monodisperse magnetic composite particles for magnetorheological fluid materials

Monodisperse magnetic composite particles (MCP) were prepared and characterized for a study of magnetic field-responsive fluids. Magnetic composite particles used are iron oxide-coated polymer composite particles, which were synthesized through in situ coating of iron oxide onto pre-existing polymer particles by the reduction of ferrous fluids. For a uniform and bulk coating of iron oxide, the porous structure was introduced into the substrate polymer particles through a two-step seeded polymerization method. Moreover, surface cyano-functionality was born from acrylonitrile unit of substrate polymer and it played an important role in obtaining successful uniform coating. The structure of the composite particle was analyzed by using a thermo gravimetric analysis (TGA) and a X-ray diffraction (XRD) analysis. The magnetization property of the particle was also observed. Then, the rheological properties of monodisperse magnetorheological (MR) suspensions of magnetic composite particles were examined under a magnetic field using a parallel-plate type commercial rheometer. From the rheological measurements, it was found that MR properties of the magnetic composite suspensions are dependent on the iron oxide content and the fluid composition.