Cellulose nanofibril enhanced ionic conductive hydrogels with high stretchability, high toughness and self-adhesive ability for flexible strain sensors.

Preparation of ion-conductive hydrogels with excellent mechanics, good conductivity and adhesiveness is promising for flexible sensors, but remains a challenge. Here, we prepare a self-adhesive and ion-conductive hydrogel by introducing cellulose nanofibers (CNF) and ZnSO into a covalently-crosslinked poly (acrylamide-co-2-acrylamide-2-methyl propane sulfonic acid) (P(AM-co-AMPS)) network. Owing to the hydrogen bonding and metal coordination interactions among P(AM-co-AMPS) chains, CNF, and Zn, the resulting P(AM-co-AMPS)/CNF/ZnSO hydrogel exhibits high stretchability (1092 %), high toughness (244 kJ m), and skin-like elasticity (3.53 kPa). Moreover, the hydrogel has strong adhesion with different substrates by multiple non-covalent interfacial interactions. The SO on AMPS and COO on CNF largely promptes the ionic migration (Zn, SO) through electrostatic interaction and hydrogen bonding, thus the hydrogel has high ion conductivity (5.85 S m). Finally, this hydrogel has high strain-sensitivity in a wide strain range, exhibiting great potential applications in wearable sensors.