Freezing-tolerant, widely detectable and ultra-sensitive composite organohydrogel for multiple sensing applications

Recently, hydrogel-based flexible sensors have attracted tremendous attention for use in wearable soft electronics. However, under sub-zero temperatures, common hydrogel-based flexible devices are always out of work due to their poor stability in freezing environments. To endow hydrogel-based sensors with long-term stability and anti-freezing ability as well as multi-functional abilities, we developed a polydopamine-reduced graphene oxide (PDA-rGO)/sodium alginate (SA)/polyacrylamide (PAM) composite organohydrogel with dual crosslinking networks. The excellent conductivity of the organohydrogel is due to the well-dispersed rGO endowed by mussel-inspired chemistry and ions such as Ca2+, which give the organohydrogel strain, pressure, and temperature sensing capabilities with a high gauge factor (2.09) within a broad strain range (0-250%), short response time (200 ms), and a wide temperature detection range (-20 °C to 60 °C), respectively. Moreover, the assembled sensors can also detect multiple human motions such as finger bending, facial micro-expression, and hand gesture recognition. Especially, owing to the synergistic effects of ion transportation, water-glycerol binary solvent, and the reduced graphene oxide in the composite hydrogel, the organohydrogel achieved an unprecedented thermal sensitivity of 97.60% °C-1 at sub-zero temperatures, which is the most sensitive stretchable thermistor so far reported. Therefore, this as-prepared functional organohydrogel paves the way for potential applications in human-machine interactions and personalized multi-signal monitoring in a broad temperature range.