Tough, highly resilient and conductive nanocomposite hydrogels reinforced with surface-grafted cellulose nanocrystals and reduced graphene oxide for flexible strain sensors

Conductive hydrogels have drawn much attention in the field of flexible strain sensors. However, it remains challenging to fabricate conductive hydrogels with simultaneous high toughness and high resilience. Herein, we present a facile method to fabricate tough, highly resilient and conductive nanocomposite hydrogels, i.e. introducing poly(N-vinylpyrrolidone) grafted cellulose nanocrystal (CNC-g-PVP) and poly(acrylic acid) grafted reduced graphene oxide (rGO-g-PAA) into chemically crosslinked polyacrylamide (PAM) hydrogel networks through in-situ free radical polymerization. The synergistic reinforcement effect of CNC-g-PVP and rGO-g-PAA brings the nanocomposite hydrogels high toughness under stretching, and low hysteresis and high resilience ( > 95%) during cyclic tensile loading-unloading. The well-dispersed rGO-g-PAA endows the nanocomposite hydrogels with satisfactory electrical conductivity (5.3-8.3 x 10(-4) S/m) and obvious resistance change under stretching. The hydrogel-based strain sensors exhibit good cycling stability and repeatability because of the high resilience of hydrogels. The combination of conductivity, toughness and high resilience makes the nanocomposite hydrogels good choice for flexible strain sensors.