Broadband and pixelated camouflage in inflating chiral nematic liquid crystalline elastomers

Abstract

Living organisms such as fishes¹, cephalopods² and clams³ are cryptically coloured with a wide range of hues and patterns for camouflage, signalling or energy regulation. Despite extensive efforts to create colour-changing materials and devices⁴, it is challenging to achieve pixelated structural coloration with broadband spectral shifts in a compact space. Here, we describe pneumatically inflating thin membranes of main-chain chiral nematic liquid crystalline elastomers that have such properties. By taking advantage of the large elasticity anisotropy and Poisson's ratio (>0.5) of these materials, we geometrically program the size and the layout of the encapsulated air channels to achieve colour shifting from near-infrared to ultraviolet wavelengths with less than 20% equi-biaxial transverse strain. Each channel can be individually controlled as a colour 'pixel' to match with surroundings, whether periodically or irregularly patterned. These soft materials may find uses in distinct applications such as cryptography, adaptive optics and soft robotics.