Chiral Photonic Crystalline Microcapsules with Strict Monodispersity, Ultrahigh Thermal Stability, and Reversible Response

Tunable photonic crystals (TPCs) reflecting selected wavelengths of visible light and responding to external stimuli are widely applied to fabricate smart optical devices. Chiral nematic liquid crystals (CNLCs) possessing response to temperature, electric field, and magnetic field are considered as one-dimensional TPCs. The encapsulation of CNLCs provides responsive photonic devices with stand-alone macroscopic structure and excellent processability. However, when CNLCs as cores are wrapped by polymeric shells to form core-shell structured microcapsules, the polydispersity of microcapsule size, the irregular spatial geometry, and the low thermal stability inevitably result in a deterioration of the optical performance and limited application at high temperatures. Herein, a combination of microfluidic emulsification and interfacial polymerization is employed to fabricate polymer wrapped photonic crystalline microcapsules (PWPCMs). The sizes and reflected colors of PWPCMs can be simultaneously controlled by adjusting the flow rates in the microfluidic chips. PWPCMs possess strictly monodispersed sizes with coefficients of variation less than 1%. The free-standing PWPCMs have high thermal stability. The deformation temperature of PWPCMs is as high as 210 °C. The colored PWPCMs also exhibit a reversible thermochromic property between the chiral nematic phase and the isotropic phase. The highly stable and tunable PWPCMs provide new opportunities for a wide range of photonic applications, including smart optical window, tunable microlasers, responsive microsensors, and various photonic devices.