Rapid preparation of size-tunable Fe 3 O 4 @SiO 2 nanoparticles to construct magnetically responsive photonic crystals

Superparamagnetic Fe 3 O 4 @SiO 2 with regular core–shell structure, controllable size, and high saturation magnetization (Ms) were prepared as the building blocks to construct magnetically responsive photonic crystals (MRPCs). A simple, rapid, and feasible procedure to self-assemble the core of Fe 3 O 4 colloidal nanoclusters (CNCs) was accomplished through miniemulsification and evaporation. Subsequently, the shell of SiO 2 was prepared by a modified Stöber method. The sizes of Fe 3 O 4 CNCs could be controlled easily by tuning emulsifier SDS concentrations, the phase ratio of oil to water, and the amount of OA-Fe 3 O 4 . The size of Fe 3 O 4 CNCs could be tuned from 76.8 to 151.8 nm expediently. The Fe 3 O 4 CNC with a size of 99.1 nm was chosen as the magnetic core for the fabrication of Fe 3 O 4 @SiO 2 nanoparticles because of a strong saturation magnetization and an appropriate size. Moreover, the amount of TEOS added in Stöber system was also an important parameter, which influenced SiO 2 shell thickness and Ms. TEM images and hysteresis loops showed that as the amount of TEOS ranged from 0.3 to 1.5 mL, the thickness of SiO 2 shell increased from 14.72 to 22.31 nm, and the Ms decreased from 47.01 to 35.2 emu·g −1 . Obviously, the increase of shell thickness also resulted in a red shift of the structural color of Fe 3 O 4 @SiO 2 colloidal photonic crystals. This work provided a quick and gentle approach to prepare Fe 3 O 4 CNCs with a high Ms and a controllable size, which makes regulation of the structure color of MRPCs simplified. Graphical abstract