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.