Self-adaptive high-temperature gels with long-lasting underwater stability for environmentally tolerant flexible sensors and water-writing papers

Hydrogel-based flexible electronics have received increasing attention owing to the requirement in a variety of applications. However, the design and development of underwater and self-adaptive high-temperature strain sensors remain a significant challenge because of the swelling and dehydration of hydrogels in aquatic environments and extreme climate conditions. Herein, a versatile gel with superior self-adhesiveness, long-lasting underwater stability, excellent high-temperature tolerance and long-term non-drying properties is successfully prepared, which can serve as a wearable sensor for precisely and reliably detecting diverse body movements and the direction of human movements in air and aquatic environments. Meanwhile, based on the Morse code expression, the as-fabricated gel sensor can also be utilized as a wearable communication device for delivering various messages to the receiver. Furthermore, a wireless sensor with high-temperature adaptability is constructed, which can transmit in real time the motion signals at high temperature to the specific APP of a smartphone at room temperature via wireless communication. This strategy provides a new perspective and great convenience for motion monitoring under harsh conditions. In particular, the as-prepared gel demonstrates an obvious transparency-shifting behavior in different polar solvents, thus inspiring us to engineer it as a novel water-writing paper for achieving repeatable “writing–erasing” applications.