Asymmetric and Skin-Mimicking Hydrogels with Wide Temperature Tolerance and Superior Elasticity for High-Performance Strain Sensors.

Wide temperature tolerance and superior mechanical properties are highly required for composite hydrogels in electronic applications such as electronic skins and soft robotics. In this work, a unique polyacrylamide-based and double-network hydrogel system is designed and fabricated by introducing graphene oxide and glycerol to improve mechanical properties as well as antifreezing and antiheating properties. Maximum stress of the graphene oxide-incorporated hydrogel increases rapidly to 500.0 kPa which is much higher than that of polymetric acrylamide/carboxymethylcellulose sodium hydrogel (281.7 kPa), probably due to the inhibition from graphene oxide in generation and propagation of cracks. With constantly adding glycerol, total elongation and antifreezing and heating properties of the composite hydrogels increase gradually. Especially, sample with 20 vol % of glycerol not only shows stable conductivity and wide temperature tolerance (-50 to 50 °C) but also has ideal strength-toughness match (597.6 kPa and 1263.4%), suggesting that synergistic effect of different layers in the asymmetric structure plays an active role in improvement of mechanical properties.