Structural Color Mixing in Single-Pitched Cholesteric Liquid Crystals with Dimple Arrays via Dual Retroreflection Pathways

Abstract

Cholesteric liquid crystals (CLCs) exhibit structural colors through selective reflection at their photonic stopband. However, their single-band reflection within the visible spectrum restricts accessible color diversity. While multiple helical pitches can broaden the palette, such approaches typically require complex, multilayered fabrication processes. Here, we report a bioinspired strategy that generates two distinct reflection bands from a single-pitched CLC film, enabling juxtaposition-based color mixing. Drawing inspiration from the dual retroreflection mechanism of Papilio palinurus, we integrate CLCs with a dome-down poly(vinyl alcohol) (PVA) microdome array to form a periodic dimple architecture. The curved PVA domes induce planar alignment of LC molecules, orienting the helical axes radially and establishing two distinct optical pathways: single normal reflection at the dimple bases and interstitial regions and oblique double reflection at the dimple rims with an apparent 45° angle. These spatially separated dot, background, and rim features merge into a unified mixed hue in the far field. By adjusting chiral dopant concentration and dimple areal density, the base wavelength of the CLC stopband and the relative intensity balance between the two reflection pathways can be tuned, enabling near-infrared/visible, visible/visible, and ultraviolet/visible combinations. This single-pitch, dual-pathway design provides a scalable and versatile platform for adaptive photonic coatings, angle-robust displays, and high-security anticounterfeiting.