Magnetorheological Fluids with Surface-Modified Iron Oxide Magnetic Particles with Controlled Size and Shape

This study is focused on surface-modified Fe₃O₄@SiO₂ particles with precisely controlled sizes and shapes applied in magnetorheological (MR) fluids. After the preparation of the monodisperse spindle-shaped and cubic Fe₃O₄@SiO₂ particles, surface modification with dodecyltrimethoxysilane (DTM) was carried out via a silane coupling reaction to increase the dispersion stability of the particles. Afterward, MR fluids were prepared by mixing the DTM-modified Fe₃O₄@SiO₂ particles with silicon oil. Transmission electron microscopy observations demonstrated that spindle-shaped Fe₃O₄@SiO₂ particles could form a more stable chain-like structure than cubic Fe₃O₄@SiO₂ particles upon application of an external magnetic field. The rheological measurements of MR fluids also indicated that the surface modification with DTM, the introduction of anisotropic shapes, and the increase in the particle size all played positive roles in the improvement in MR properties.