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. Transmission electron micrograph for magnetite polystyrene particles (Latex‐1).