Electrically Conductive Zwitterionic Hydrogel with Extraordinary Antifreezing Performance

Hydrogels have found wide applications in electronic skin, flexible sensors, and soft robots owing to many unique properties. However, the performances of hydrogel suffer drastic deterioration at subzero temperature, as the result of water freezing within the hydrogel network. To address this challenge, a new type of zwitterionic hydrogel filled with cysteine-rich carbon nanotubes is fabricated. The cationic and anionic counterions on zwitterionic poly(sulfobetaine methacrylate) (PSBMA) chains bound closely with water molecules to inhibit ice nucleation, while cysteine-decorated multiwalled carbon nanotubes (MWCNTs-Cys) effectively inhibit ice nucleation and suppress ice growth, achieving hydrogels with freezing tolerance over a wide temperature range from −60 to 25 °C. The obtained MWCNTs-Cys/PSBMA hydrogels exhibit a high stretchability of 1671% and elasticity above 98% at 25 °C, as well as excellent tensile flexibility of above 1000% even at −45 °C. Owing to the synergistic effect of zwitterionic polymer chains and MWCNTs-Cys, the hydrogels possess high conductive sensitivity for a wide range from 25 to −40 °C, making it promising to be used for wide temperature range strain sensors.