Designing hyper-reflective colloidal photonic crystals with narrow bandwidth via shear-induced colloidal rearrangement

Abstract

Colloidal crystallization serves as one of the most economic and scalable production methods for photonic crystals. However, insufficient optical performance and low uniformity and reproducibility remain challenges for advanced high-value applications. In this study, we optimally formulate a photocurable dispersion of silica particles and apply shear flow to unify the orientation of colloidal crystals, ensuring high optical performance and uniformity. The silica particles experience strong repulsion at ultrahigh volume fractions of 50%, but demonstrate low mobility, leading to polycrystalline structures. Applying shear flow to the dispersions allows the silica particles to rearrange into larger crystalline domains with a unidirectional orientation along the flow. This shear-induced structural change produces absolute reflectivity at the stopband as high as 90% and high transparency of 90% at off-resonant wavelengths with minimal diffusive scattering. Furthermore, strong interparticle repulsion ensures a uniform volume fraction of particles throughout the dispersion, reducing deviations in optical properties. We intricately micropattern the photocurable dispersions using photolithography. Additionally, the photonic films and patterns can be stacked to form multiple layers, displaying mixed structural colors and multiple reflectance peaks without sacrificing reflectivity. These superior photonic materials hold promise for various optical applications, including optical components and anti-counterfeiting patches.