Recent advances in multifunctional shape memory photonic crystals and practical applications

Shape memory photonic crystals (SMPCs) are smart composite materials with changeable structural color integrated by shape memory polymer and photonic crystals. SMPC can produce one or more temporary shapes through nanoscale deformation, memorizing current states. SMPC can be recovered to their original shapes or some intermediate states under external stimuli, accompanied by the variation of structural color. As porous carriers with built-in sensing properties, SMPCs promoted the interdisciplinary development of nanophotonic technology in materials science, environmental engineering, biomedicine, chemical engineering, and mechanics. Herein, the recent progress on multifunctional SMPCs and practical applications, including traditional and cold programmable SMPCs, is summarized and discussed. The primary concern is shape programming at the nanoscale that has demonstrated numerous attractive functions, including smart sensing, ink-free printing, solvent detection, reprogrammable gradient wetting, and controllable bubble transportation, under variations of the surface nanostructure. It aims to figure out the nanoscale shape memory effects on structural color conversion and additional performance, inspiring the fabrication of the next generation of SMPCs. Finally, perspectives on future research directions and applications are also presented. It is believed that multifunctional SMPCs are powerful nanophotonic tools for the interdisciplinary development of numerous disciplines in the future.