Facile fabrication of Janus magnetic microcapsules via double in situ miniemulsion polymerization

We describe a facile and flexible technique for fabricating Janus magnetic microcapsules via double in situ miniemulsion polymerization. Under a magnetic field, magnetic nanoparticles move to one side of the miniemulsion monomer droplets. After the monomers polymerize, an inorganic tetraethoxysilane (TEOS) phase is compressed and restricted as a liquid core due to the phase separation between TEOS and the growing polymer. After the monomers turn into a polymeric shell and the silica forms completely, the volume of the TEOS phase decreases dramatically leading to a hollow structure. Magnetic nanoparticles are chemically embedded in one side of the microcapsule shell and Janus magnetic microcapsules are fabricated efficiently and conveniently by a one-step method.