Complex-Shape Solid-State Photonic Droplets Prepared via Phase Separation and Microfluidics

Complex-shape solid-state cholesteric liquid crystal (CLC_solid) droplets were prepared via solvent removal, phase separation, and photopolymerization of uniformly sized reactive CLC (rCLC)/fluorocarbon oil (FCO)/dichloromethane (solvent) droplets produced via a microfluidic method. The interfacial energies between rCLC and FCO, rCLC and water, and FCO and water of a rCLC/FCO droplet in an aqueous solution were precisely controlled through the specified surfactants. The shape of the rCLC/FCO droplet was strongly dependent on the balances among these interfacial energies, enabling the preparation of complex-shape droplets through the controlled concentration of the used surfactants. The complex-shape rCLC/FCO droplets showed photonic patterns consisting of a central reflection from a convex surface, cross-communication from a convex surface between adjacent particles, a photonic reflection band from the outer upward-facing concave surface, and total internal reflection from the inner upward-facing surface. Complex-shape CLC_solid particles obtained after photopolymerization and extraction of a nonreactive chiral dopant and FCO showed photonic patterns similar to those before photopolymerization without much deterioration of the photonic structure. These complex patterns make CLC_solid and rCLC/FCO droplets promising anticounterfeiting materials.