Magnetic polystyrene nanoparticles with a high magnetite content obtained by miniemulsion processes

The encapsulation of high amounts of magnetite into polystyrene particles can efficiently be achieved by a new three-step preparation route including two miniemulsion processes. In the first step, a dispersion of oleic acid coated magnetite particles in octane is obtained. In the second step, magnetite aggregates in water are produced in a miniemulsion process by using sodium dodecyl sulfate (SDS) as surfactant. In the third step, the dispersion with the magnetite aggregates which are covered by an oleic acid/SDS bilayer were mixed with a monomer miniemulsion and a second miniemulsion process, an ad-miniemulsification process, is used to obtain full encapsulation. After polymerization, polymer encapsulated magnetite aggregates were obtained. Characterization by thermogravimetry, preparative ultracentrifugation, and transmission electron microscopy showed that up to 40% magnetite could be encapsulated resulting in particles with a high homogeneity of the magnetite content. Magnetometry measurements reveal that the included iron oxide aggregates still consist of separated superparamagnetic magnetite particles.