Near-Infrared Laser “Weldable” Hydrogen-Bonded Hydrogel Sensor Based on Photothermal Gel–Sol Transition

As a flexible conductive material, the conductive hydrogel has been extensively studied in the field of sensor materials. However, there are still insufficient research studies on the recyclability and repairability of high-strength conductive gel materials. In this work, we synthesized an N-acryloylglycinamide monomer and further synthesized a hydrogen-bonded hydrogel, with a photothermal agent, and used glycerin and water as a mixed solvent to obtain a hybrid gel with good mechanical properties. The tensile strain reached 436%, and the stress reached 0.728 MPa. The conductivity of the gel reached 0.026 S/m, and its sensitive and accurate stress conductivity changes could meet the requirements of some sensor materials such as wearable devices, and the good moisturizing and frost resistance properties ensured long-term stable useability. Most importantly, the composite gel could be recycled and reshaped many times through simple heating and just cooling at room temperature, showing good recyclability and reusability. The most interesting thing is that due to the addition of the photothermal agent, the composite gel showed good photothermal properties. Thus, the temperature of the gel rapidly rose to the gel–sol transition temperature under near-infrared laser irradiation, and the gel rapidly healed at room temperature. Therefore, the gel showed unique and efficient "weldability". The good thermal and photothermal recycle/repair capabilities could greatly expand the usability of gel materials, which not only increases the durability of the material but also reduces the waste of polymer materials to achieve the purpose of protecting our environment and sustainability.