Iron nanoparticles encapsulated in poly(AAm-co-MAA) microgels for magnetorheological fluids

Iron nanoparticles have plenty of applications in different areas. However, iron nanoparticles are easy to be oxidized and difficult to be prepared. In present study, the iron nanoparticles were prepared via in situ reduction with iron (II) ion as precursors and the void of poly(AAm-co-MAA) microgels as the template. The diameters of the iron nanoparticles shown by TEM are from 5 to 20 nm. Moreover, the diameters of the swollen poly(AAm-co-MAA) microgels in alcohol with iron nanoparticles inside detected by Laser Particle Size Analyzer and field emission scanning electron microscope (FESEM) are approximately 9–30 μm. The weight increasing of the composite particles in TGA results also proves the presence of iron nanoparticles in the microgels. The saturation magnetization (Bs) of the composite particles is 2.7 emu/g, and the coercive force (Hc) is 63.1 Oe when the content of iron nanoparticles in the composite particles is 16.4 wt%. This indicates that the composite particles exhibit soft magnetic properties. The sedimentation ratio of the composite particles in water is about 10% after reaching final equilibrium when the content of the composite particles is 0.032 g/mL. The apparent viscosity of the swollen composite particles in water increases with increasing intensity of the external magnetic field, which indicates the significant magnetorheological properties.