Composite photonic microobjects with anisotropic photonic properties from a controlled wet etching approach

Abstract

Colloidal photonic microobjects with anisotropic properties find diverse applications, from building blocks of tunable displays to miniaturized optoelectronic devices. Microfluidics is a robust platform for the construction of colloidal photonic microobjects. Generally, creating colloidal photonic microobjects with Janus structures via microfluidics involves either injecting different colloidal photonic streams to form Janus photonic microbjects or applying a selective coating of a metallic layer to one side of the as-prepared photonic microobjects. However, those approaches either are time-consuming or may pose negative impact on the photonic properties of the photonic microobjects. In this report, we introduce a facile yet highly reproducible approach to fabricate photonic microobjects with Janus photonic property. To achieve this, colloidal photonic microspheres that are composed of a photonic resin dispersion of single-sized SiO2 nanoparticles (NPs) are prepared via a single emulsion-based microfluidics. Subsequently, one hemisphere of each microsphere is embedded into a polystyrene (PS) film, serving as a protection matrix. The microspheres embedded PS film is overturned and placed in a controlled amount of HF solution to etch the SiO2 NPs in the unprotected domain, yielding Janus photonic microobjects. The ratio of opal to inverse-opal structure on the surface of the photonic microobjects can be accurately controlled by playing the etching parameters. The porous structure of the etched part of the microobjects can be further functionalized by polymer infiltration, featuring the microobjects with fluorescence property. These multifunctionalized microobjects may find potential applications in the fields of advanced pigments, anticounterfeiting materials, etc. This strategy paves a facile way for the design and construction other miniaturized devices.