Tunable Janus colloidal photonic crystal supraballs with dual photonic band gaps

Abstract

Methods allowing Janus particles to exhibit multiple structural colors are highly desirable. Here a new easy-to-perform strategy for fabrication of series of Janus supraballs (JSs) with dual photonic band gaps (PBGs) is demonstrated, through triphase microfluidic assembly of two kinds of different colloidal photonic crystals (CPCs) into a single JS. Using monodispersed PS and SiO₂ colloidal particles as building blocks, polystyrene (PS)/SiO₂ Janus and PS@SiO₂ core–shell supraballs were prepared by governing the surface tensions between the two immiscible components, to display dual structural colors. Dual-PBG PS/Fe₃O₄ JSs were further fabricated, wherein the Fe₃O₄ hemisphere constructed from superparamagnetic monodispersed Fe₃O₄ colloidal particles exhibits magneto-tunable structural color, overcoming the dull color of JSs with common Fe₃O₄ particles. More importantly, PS/Fe₃O₄ JS-based bead panel displays have dual-color properties, which can respond to strong and weak visible light resulting from optical differentiations between PSs and Fe₃O₄ CPC hemispheres, showing obvious switchable behaviors. This method may be extended to create various dual photonic materials.