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.
Keywords: mechanochromic; photonic crystals; reversibility; self-assembly; shape memory.