Highly charged, magnetically sensitive magnetite/polystyrene colloids: synthesis and tunable optical properties

Highly charged monodisperse magnetite/polystyrene colloidal particles are successfully synthesized by using a miniemulsion polymerization method. The particles, with high saturation magnetization (M_s ≈ 38.6 emu g⁻¹), display high sensitivity to the magnetic field and can self-assemble into periodically ordered colloidal structure in aqueous solution, thus diffract light strongly, under magnetic induction. By changing the strength of magnetic field, the position of reflection peaks can be reversibly tuned in the range of 420–720 nm, covering almost the entire visible light range. After adding 1.5 wt.% of acid black 210 into the colloidal suspension, the color saturation and brightness of the colloids are significantly improved. As-prepared magnetically responsive colloidal particles have great potential to be used in color display, biosensors, anti-counterfeiting, camouflage, pigments and dyes.