High-Reflectivity Force-Chromic Photonic Crystal Elastic Materials Based on Nanospheres within an Elastomer for Applications in Sensing and Textile Fields

Abstract

By mimicking the biological process in which chameleons change the lattice spacing of guanine nanocrystals to form and regulate their skin color, scientists have prepared force-chromic photonic crystal materials (FPMs) by encapsulating arrays of photonic crystal nanospheres in elastic matrices. However, the low refractive index difference (Δn) between conventional nanospheres and elastic matrix combinations typically makes the photonic material transparent and with low color reflectance. Besides, the elastic matrix is mostly dominated by hydrogel materials, which gradually decrease or even lose the stability of the sensing material as the solvent evaporates. PS@SiO₂ core–shell nanospheres with a high refractive index while reducing the risk of microplasticity are ideal for preparing FPMs. In this work, we explored the preparation method of PS@SiO₂ nanospheres and prepared force-chromic photonic crystal elastomers (FPEs) by embedding them into di(ethylene glycol) ethyl ether acrylate (DEGEEA) and polyethylene glycol monophenyl ester acrylate (PEGPEA) matrices via the coassembly method. It was found that due to the large Δn between PS@SiO₂ nanospheres and acrylate matrices (Δn > 0.05), the FPE possessed a high reflectivity (R > 82%), and the color change under force stimulation is obvious. Meanwhile, the FPE had a good tensile strain and a high sensitivity (1.62 nm/%). Due to the absence of solvents in the elastic system, the FPE has excellent stability, and the structural color remains unchanged under 50 stretch/release cycling experiments. This FPE not only has a simple preparation method, fast response, high reflectivity, and good stability, but we have found through validation experiments that it has great potential in the fields of sensing, signal transmission, and smart textiles.