Strategy Based on Rapid Self-Assembly of Magnetic Nanoparticles for Construction of Photonic Crystals

A convenient, fast strategy based on self-assembly was developed to prepare polymer-coated Fe3O4 magnetic colloidal nanoparticles (MCNPs) for the construction of magnetically responsive photonic crystals (MRPCs). In this strategy, oleic acid (OA)-modified Fe3O4 nanoparticles dispersed in chloroform as an oil phase were finely emulsified by an amphiphilic random copolymer P(MMA-co-MAA) as an emulsifier. Both the magnetic nanoclusters and the P(MMA-co-MAA) coatings completely self-assembled simultaneously along with the evaporation of chloroform. MCNPs were formed rapidly within 0.5 h through ultrasonic miniemulsification and rotary evaporation processes. Transmission electron microscopy (TEM) showed that MCNPs possessed a regular spherical structure with an average particle size of 105.0 nm and a low polydispersity of 0.024. A high Fe3O4 content of 84.48 wt % and thin polymer coatings endowed MCNPs with a high saturation magnetization (Ms) of 69.96 emu·g–1. Under an external magnetic field, MCNPs could be magnetically assembled to build MRPCs instantaneously and reversibly. The structural color of MRPCs was finely controllable by adjusting the strength of the magnetic field, and the reflection wavelength could be modulated covering the entire visible spectrum. This work provides an efficient and quick approach to prepare MCNPs with a high Ms and a controllable size, which would expand the application of MRPCs.