A tough and piezoelectric poly(acrylamide/N,N-dimethylacrylamide) hydrogel-based flexible wearable sensor

A flexible, tough, highly transparent and piezoelectric polyacrylamide hydrogel was fabricated induced by blue light photocuring, with camphorquinone/diphenyliodonium hexafluorophosphate (CQ/DPI) as the blue light initiator, acrylamide (AM) and N,N-dimethylacrylamide (DMAA) as monomers, polyethylene glycol diacrylate (PEGDA) as the crosslinker, lecithin as the dispersant, and BaTiO3 as the piezoelectric material. Various performance tests were carried out on the hydrogel, and the results showed that lecithin enhances the dispersion of BaTiO3 within the system and improves the tensile properties (>100% strain) of the hydrogel, and the addition of PEGDA not only improves the photopolymerization performance of the hydrogel, but also significantly improves its fracture strength (similar to 0.3 MPa). In addition, BaTiO3 enables the resultant hydrogels to show excellent conductivity (>1.5) and stable response to strain. The assembled hydrogel sensor shows a sensitive response to human joint activities, which is expected to be applied in self-powered sensors and energy collection.