Nanocellulose-toughened super-stretchable ionic conductive gel fibers for wearable strain sensors.

In recent years, conductive gel materials have attracted extensive attention in the field of flexible electronics because of their excellent elasticity. When constructed as gel fibers, they can adapt to greater deformation, be woven, and be assembled with fabrics to make wearable smart devices without compromising comfort. However, gel fibers reported often exhibit insufficient mechanical properties and poor adaptability to different environment. Herein, a super-stretchable ionic conductive gel fiber is reported. It is formed via a solvent-free template-assisted strategy, with a polyacrylamide (PAM) - TEMPO-mediated oxidized cellulose nanofibrils (TOCNF) double-network as main structure. The influence of each component content was analyzed. The addition of TOCNF significantly toughens the fiber (breaking strength, strain and toughness of 3.55 MPa, 1715.66 % and 4.75 MJ/m, respectively) and provides larger channels for ion transport. The synergistic effect of lithium chloride (LiCl) and glycerin in system endows the fiber with properties of anti-dehydrating, anti-freezing, and good ionic conductivity (0.128 S/m). When used as a wearable strain sensor, the gel fiber has good linear response (sensitivity gauge factor of 0.8128) in the strain range of 0-300 %, which can accurately and stably sense human body movement, such as finger bending, wrist activities, walking and running in real time.