Mechanochromic and thermochromic shape memory photonic crystal films based on core/shell nanoparticles for smart monitor

Shape memory photonic crystal (SMPC) combining main characteristics of shape memory materials and photonic crystals have drawn increasing research interests. In sharp contrast with traditional responsive photonic crystals, temporary shape of SMPC can be “frozen” and photonic configurations can be modulated by temperature. However, large-scale fabrication of SMPC still remains a big challenge, making the practical application difficult. Herein novel scalable SMPC films with both mechanochromic and thermochromic properties are reported. Unlike traditional template-based methods resulting in only a small size, the SMPC film are fabricated by facile hot-pressing method and post-photocuring technology to give large-area freestanding polymer films. The films are mechanically robust and flexible, featuring excellent structural color which can be changed upon stretching, similar to color change process of chameleon in response to environment. Blue-shift of reflection peak up to 120 nm can be observed when the film is stretched. The films can be reversibly stretched and recovered in 25 cycles without obvious changes in reflection spectra. The temporary shape accompanied by tremendous color changes of corresponding SMPC films after mechanical stress induced hot programming could be simply fixed by cooling the structure below the glass transition temperature of the polymer matrix. Incorporate programmed optical properties could afterwards be erased by temperature, and initial optical properties could be fully restored. Based on the fully reversible programmable shape as well as optical properties, the investigated SMPC films are expected to be promising candidates for various potential applications, such as smart monitor, sensors, anti-counterfeiting, and display.