Highly Stretchable, Tough, and Self-Recoverable Cationic Guar Gum-Based Hydrogels for Flexible Sensors

Stretchable and tough conductive hydrogels have attracted much attention in flexible sensing electronics. However, most existing conductive hydrogels have poor strain and strength or unsatisfactory recovery capability, which cannot satisfy the requirements for stretchable electronics. In this study, a type of hybrid ionic-covalent guar hydroxypropyltrimonium chloride (cationic guar gum, CGG)-based DN hydrogel with PAM covalent and CGG-CO32– or CGG-SO42– ionic networks via a free radical polymerization and soaking process was developed to prepare high-performance strain sensors. The existence of salt ions in the CGG-based hydrogel not only induces the formation of noncovalent cross-linking points, endowing the hydrogel high mechanical performance, but also gives the hydrogel high ionic conductivity. Consequently, the obtained hybrid DN hydrogels show high tensile strength (>1.2 MPa), large elongation (>1200%), high toughness, good conductivity, and rapid self-recovery property. Significantly, by simply controlling the soaking duration, we tailored the mechanics of the hybrid DN hydrogels. As demonstrated, this hydrogel-based sensor exhibits good sensitivity, large strain sensing capability, high durability, and could detect various human motions. Our study opens up a horizon in the preparation and regulation of cationic guar gum-based hydrogels for applications in high-performance flexible sensors.