Extraordinary sensitive mechanochromic hydrogels for visually detecting ultrasmall pressure

Similar to chameleon skins, colloidal mechanochromic photonic crystals (MPCs) have been receiving increasing attention due to their capability of adjusting colors by force. However, their applica-tions are hindered by poor sensitivity (<1 nm/kPa or nm/%), respon-siveness (<1 nm/ms), and tuning range of wavelength (AA < 180 nm), mainly due to the small surface-to-surface distance (Ds-s) between neighboring particles. Here, we have fabricated supersensitive SiO2/water-hydroxyethyl acrylate MPC hydrogels with large Ds-s and thus extreme sensitivity (106.9 nm/kPa and 3.7 nm/%), fast responsiveness (11.3 nm/ms), broad AA (340 nm), and good revers-ibility (>100 times) by swelling non-closely packed structures com-bined with a unique interface etching-induced swelling mechanism. The unique compositions, structures, and swelling mechanisms are the keys to precisely regulating the Ds-s and mechanochromic prop-erties. These MPC hydrogels can monitor the small jump pressure of frogs dynamically, visually, and instantly, showing their potential ap-plications in sensing and wearable devices.

Automated summary

The researchers have successfully fabricated SiO2/water-hydroxyethyl acrylate mechanochromic photonic crystal (MPC) hydrogels with high sensitivity, fast responsiveness, and broad tuning range of wavelength. By utilizing non-closely packed structures and a unique interface etching-induced swelling mechanism, the hydrogels have large surface-to-surface distances and thus exhibit improved mechanochromic properties. These MPC hydrogels can dynamically, visually, and instantly monitor the small jump pressure of frogs, showing potential applications in sensing and wearable devices.