Nanobeads Highly Loaded with Superparamagnetic Nanoparticles Prepared by Emulsification and Seeded-Emulsion Polymerization

Functional superparamagnetic colloids possessing high saturation magnetization are prepared by emulsification of superparamagnetic nanoparticles (SPM NPs) and heterogeneous polymerization. The colloids consist of a core of densely packed NPs encapsulated within a thin polymer shell. The cores are made by emulsifying SPM NPs and toluene into an aqueous surfactant solution, and subsequently condensing the emulsion droplets by removal of the solvent generating clusters of SPM NPs. By tuning the emulsification condition, this approach allows for control over the size of the clusters from approximately 40 to 200 nm. The polymer shells encapsulating the clusters are made by using seeded-emulsion polymerization concepts. Control over the thickness of the shell and the incorporation of functional groups to the colloid is achieved. Characterization by thermogravimetric analysis (TGA) and magnetometry shows that these colloids have 66 wt % of magnetic material and saturation magnetization of 47 emu/g, confirming that this route generates colloids with a high loading of SPM NPs and high saturation magnetizations.