Dual-mode, selective-adhesive and conductive hydrogel for underwater sensing

Conductive hydrogels have emerged as promising materials for wearable sensors in recent years. However, most of them have single ability to detect visual or conductive signals and exclude adhesion in water. To address these issues, polymethacrylamide/polyacrylic acid/zirconium ion/carbon quantum dots (PMAm/PAA/Zr 4+ /CQDs) hydrogels were adopted as the conductive matrix, followed by coating a gelatin-tannic acid adhesive layer at the bottom to obtain a Janus hydrogel. The Janus structure endowed the hydrogel with high strength (414 kPa) and strain (150 %), low swelling ratio (4 %), robust wet adhesion (30 N/m), and good sensing performances (with a conductivity of 5.6 S/m, and a gauge factor of 1.77), even after soaking in aqueous environments for a month. The incorporation of Zr 4+ and CQDs endowed dual visual and electrical sensing, which synchronously converted mechanical deformations into resistance variations and high-contrast optical signals. Consequently, it simultaneously provided dual-mode feedbacks for various human motions both underwater and on land. Therefore, the present work opened new avenues for the development of flexible devices for underwater sensing.