Tunable photonic crystals from emulsion containing magnetic nanoparticles

We report a simple approach to synthesize emulsion of oleic acid (OA) containing Fe₃O₄-OA nanoparticles as magnetic building block of photonic crystals by combined chemical co-precipitation and emulsification technology. The emulsion droplets exhibit dominant size distribution of 80-110 nm and superparamagnetic behavior. A high loading fraction of magnetic compounds Fe₃O₄ in emulsion of 72% was achieved by the approach. Upon application of a magnetic field, the emulsion droplets in water facilely self-assemble into photonic crystals, and the stop bands could be tuned in ranging visible spectrum by moving position of magnet. The method to synthesize emulsion with high magnetic loading fraction should facilitate preparation of tunable photonic crystals and expand their application.