Zwitterionic cellulose nanofibers-based hydrogels with high toughness, ionic conductivity, and healable capability in cryogenic environments.

Extreme environmental conditions often lead to irreversible structural failure and functional degradation in hydrogels, limiting their service life and applicability. Achieving high toughness, self-healing, and ionic conductivity in cryogenic environments is vital to broaden their applications. Herein, we present a novel approach to simultaneously enhance the toughness, self-healing, and ionic conductivity of hydrogels, via inducing non-freezable water within the zwitterionic cellulose-based hydrogel skeleton. This approach enables resulting hydrogel to achieve an exceptional toughness of 10.8 MJ m-3 , rapid self-healing capability (98.9 % in 30 min), and high ionic conductivity (2.9 S m-1 ), even when subjected to -40 °C, superior to the state-of-the-art hydrogels. Mechanism analyses reveal that a significant amount of non-freezable water with robust electrostatic interactions is formed within zwitterionic cellulose nanofibers-modified polyurethane molecular networks, imparting superior freezing tolerance and versatility to the hydrogel. Importantly, this strategy harnesses the non-freezable water molecular state of the zwitterionic cellulose nanofibers network, eliminating the need for additional antifreeze and organic solvents. Furthermore, the dynamic Zn coordination within these supramolecular molecule chains enhances interfacial interactions, thereby promoting rapid subzero self-healing and exceptional mechanical strength. Demonstrating its potential, this hydrogel can be used in smart laminated materials, such as aircraft windshields.