Robust mechanochromic elastic one-dimensional photonic hydrogels for touch sensing and flexible displays

Mechanochromic materials which control their color variation by straightforward effective mechanical stimuli are useful for applications including switches, display devices, and sensors. It is still challenging to create mechnochromic materials with wide-range color tunability, fast response, and sensitivity to pressure <10 kPa. Here a facile strategy to fabricate very sensitive and reversibly mechanochromic elastic photonic hydrogels (EPHs) is demonstrated. The hydrogels exhibit reversible full-color variation within 1 s under each compression-decompression cycle. Importantly, EPH films display versatile touch-induced chromatic behavior even under forces below 0.5 N or pressures down to 1 kPa. Furthermore, rewritable displays on EPH films are realized by the exertion of forces without any external inks. This work may provide a new way to develop smart skin materials with integrated functions of tactile sensing and color variation, as well as touch-based flexible displays. Elastic photonic hydrogels (EPHs) with one-dimensional ordered chain-like colloidal crystal arrays of magnetically active monodisperse nanoclusters are synthesized, and exhibit versatile mechanochromic behavior with advanced sensitivity and interesting potentials for touch sensing, color-based switching, and flexible displays.