Mechanofluorescent Double Network Ionogels

Mechanofluorescent gels, which are soft and capable of altering their fluorescent color in response to the applied external force, have garnered significant attention for applications spanning failure alert, crack visualization, information encryption, and adaptive camouflage. Most of the mechanofluorescent gels are obtained in the form of hydrogels, due to their facile preparation and diverse material design. However, the hydrogels suffer from compromised stability under elevated temperatures or desiccating conditions due to water evaporation. To tackle this challenge, we develop a mechanofluorescent double network (DN) ionogel that shows low volatility, high stress sensitivity, and excellent mechanical property. The ionogel is composed of two types of interpenetrating polymer networks and immobilized ionic liquids (IL) that can effectively swell the polymer chains. The resulting ionogel exhibits a reversible color change. Additionally, it demonstrates exceptional mass retention with a weight loss less than 1.5% over 15 days even at 80 °C. The mechanical property and mechanofluorescent sensitivity can be tailored via IL and mechanofluorophore content. The combination of double network structure and IL solvent overcomes the environmental instability bottleneck of mechanofluorescent gels and establishes a versatile platform for developing flexible fluorescent stress sensors.