Molybdenum disulfide enhanced polyacrylamide-acrylic acid-Fe3+ ionic conductive hydrogel with high mechanical properties and anti-fatigue abilities as strain sensors

Existing conductive hydrogels suffer from poor mechanical performance required for flexible wearable sensors. Herein, molybdenum disulfide (MoS2) nanosheet enhanced crosslinked polyacrylamide-acrylic-Fe3+ (PAAM-Fe3+) hydrogels as strain sensors were synthesized by MoS2 catalyzing the autogelation at room temperature. The obtained hydrogels possessed high tensile strength (4.19 MPa), tensile elongation (594.6 %), elasticity (1.5 MPa), and high toughness (14 MJ/m3). The prepared hydrogels also achieved high self-recovery ability; the recovery efficiency of the compression stress was 136 % within 1 min. Based on microstructure observation and mechanical behavior analysis, we demonstrated that the existence of MoS2 and FeCl3 provided reversible physical crosslinking points and that MoS2 utilized adsorption to attract more Fe3+ to enhance ionic coordination in the system, leading to significantly improved mechanical properties and fatigue resistance. The hydrogels were further demonstrated to be strain sensors with high sensitivity (with high gauge factors of 1.50 and 9.06 at subtle (<100 %) and large strains (400 %)). Moreover, the ionic sensors successfully supplied real-time feedback on the movements of the human body. Accordingly, hydrogels offer promising insights for flexible electronic devices, sensors, human health monitoring and soft robots.