Fabrication of Tunable Janus Microspheres with Dual Anisotropy of Porosity and Magnetism

This work presents a facile approach to produce a novel type of Janus microspheres with dual anisotropy of porosity and magnetism based on Pickering-type double emulsion templates. A stable aqueous Fe₃O₄ dispersion-in-oil-in-water (W_F/O/W) double Pickering emulsion is first generated by using hydrophobic silica and hydrophilic mesoporous silica particles as stabilizers. Janus microspheres with multihollow structure possessing magnetite nanoparticles concentrated on one side of the microspheres are obtained after polymerization of the middle oil phase of the double emulsion under a magnetic field. The resultant Janus microspheres are characterized by optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray analysis (EDX). Moreover, we have systematically investigated the influences of Fe₃O₄ particle concentration, hydrophobic silica particle content, and volume ratio of the inner water phase to middle oil phase (W_F/O) on the double emulsion formation and consequently on the structure of the resulting Janus microspheres. Our results show that the distribution of the multihollow structures within the prepared microspheres can be accurately tailored by adjusting the ratio of W_F/O. In addition, the obtained Janus microsphere can be fairly orientated under a magnetic field, making them a potential candidate for synthesizing Janus membrane