Preparation of monodispersed hybrid nanospheres with high magnetite content from uniform Fe3O4 clusters

Hybrid nanospheres with controllable magnetite content and narrow size distribution, composed of Fe3O4 nanoparticles encapsulated in a crosslinked polystyrene matrix, were synthesized by magneto-template (Fe3O4 minidroplets) miniemulsion polymerization. In this process, a magnetic fluid (ferrofluid), consisting of Fe3O4 nanoparticles dispersed in octane, was directly emulsified in the presence of sodium dodecyl sulfate under ultrasonication. The formation of Fe3O4 minidroplets served as a template (magneto-template) for the subsequent miniemulsion polymerization. Transmission electron microscopy (TEM) images showed uniform hybrid nanospheres in which the Fe3O4 nanoparticles were evenly dispersed. The average size of these magnetic hybrid nanospheres can be rationally adjusted from 70 nm to 130 nm by varying the amount of surfactant. The magnetite content can be controlled over a wide range, from 40 wt % to 70 wt %, by modulating the dosage of the ferrofluid. Real-time monitoring of the size of the Fe3O4 minidroplets after addition of monomers indicated gradual incorporation of monomers into the magneto-template prior to polymerization. The use of divinyl benzene with styrene to crosslink the polymer matrix was used for enhancing the integrity of the hybrid nanospheres. These magnetic hybrid nanospheres are superparamagnetic, and thus are ideal candidates for biomedical applications after suitable surface modification.