Self-Assembled Mechanochromic Shape Memory Photonic Crystals by Doctor Blade Coating

Mechanochromic shape memory photonic crystals can memorize their original structures and recover the inherent structural colors in response to external stimuli; thereby they have rendered various important optical applications. Unfortunately, most existing shape memory polymers are thermoresponsive, and the corresponding mechanochromic characteristics are limited by the heat-demanding programming process. Besides that, a great majority of current fabrication methodologies suffer from low throughput, hindering the practical applications. Herein, a scalable technology is developed to engineer macroporous shape memory photonic crystals by self-assembling silica colloidal crystals in a polyurethane acrylate/polyethoxylated trimethylolpropane triacrylate/poly(ethylene glycol) diacrylate matrix, followed by a wet etching treatment to selectively remove silica colloids. The as-created photonic crystals display a brilliant structural color, which is reversibly tunable with mechanical deformation at ambient conditions. Upon stretching, the reduced interlayer lattice spacing of the photonic crystals leads to a blueshift of the reflection peak position and a significant color change. Importantly, the stretched macroporous film can fix its temporary structures without applying any contact force and simultaneously recover its original configuration and appearance by applying ethanol evaporation-induced capillary pressures. The reversibility and the dependence of templated silica colloid size on mechanochromic characteristics have also been investigated in the research.