Dual-Bandgap Janus Photonic Crystals from Single Emulsion Droplets: Rapid Preparation and Structurally Controllable Strategies

Janus photonic crystal microspheres (PhCMs), capable of exhibiting multiple structural colors, hold immense promise in practical applications. However, devising a simple and efficient approach for fabricating highly stable Janus PhCMs with multiple stop band gaps. In this report, we propose a straightforward and controllable strategy to assemble dual-stop bandgap Janus PhCMs. A T-shaped microfluidic chip was employed to synthesize single-emulsion resin-based PhCMs (ETPTA@SiO2; PEGPA@SiO2) with an opal structure. Through a series of processes involving partial embedding within a PS protection membrane, selective HF etching, and PS membrane removal, the partial opal structure was transformed into an inverse-opal structure, resulting in an integration of both opal and inverse-opal structures on single-emulsion PhCMs. These Janus PhCMs with anisotropic structures exhibit both red and green structural color. To achieve the controllable design of Janus PhCM, diverse preparation methods have been developed during the embedding process of the PS film. Meanwhile, we propose the devise manipulation techniques for removing PS films from single-emulsion resin-based PhCMs with varying surface hardness, which greatly improves the applicability of our strategy. Our findings pave the way for the straightforward and controllable construction of Janus PhCMs, expanding their potential for future applications.