Porous Fe3O4 submicron particles for use in magnetorheological fluids

Abstract The magnetorheological (MR) performance and stability of various suspensions based on core-shell-structured polystyrene(PS) / Fe3O4 particles, the Fe3O4-coated particles, the hollow and porous Fe3O4-particles were investigated by using a rotational rheometer and Turbiscan, while magnetic properties of all the magnetic particles used were examined by using a vibrating sample magnetometer (VSM). The PS (core)/Fe3O4(shell) was synthesized by the Pickering-emulsion polymerization method using Fe3O4 nanoparticles as a solid surfactant. Hollow and porous Fe3O4 nanoparticles were obtained after extraction of the core PS phase by Soxhlet extractor. The density of the hollow Fe3O4 nanoparticles was markedly decreased compared to that of pure Fe3O4, but slightly increased compared to that of the PS/Fe3O4 particle. All suspensions, prepared by dispersing the synthesized particles in the liquid medium (silicone oil), exhibited similar MR behaviors, but the MR performance of the hollow and porous Fe3O4 particle suspension was remarkably better than that of the PS/Fe3O4 particle suspension. The hollow Fe3O4 particle suspension showed a significantly better stability than the pure Fe3O4 particle suspension due to the reduced density mismatch between the particle and the liquid medium and the rough and bumpy surface morphology. The optimal density for the MR performance and the suspension stability was determined from the MR property analysis.