Highly sensitive, anti-freeze, and ion-conductive polyelectrolyte-based hydrogel for flexible sensor applications in sub-zero temperatures

Conductive hydrogels are typically unable to function in cold environments because they freeze at subzero temperatures. A hydrogel based on an organic polyol or ionic liquids (ILs) may improve anti-freezing properties, but the integration of a single component can reduce long-term conductivity. Through the combination of glycerol and ILs in this research, we developed an anti-freeze-conducting hydrogel by leveraging the ability of glycerol to retain water and ILs' high electrical conductivity at low temperatures. As a result of the polyhydroxyl groups present in glycerol, it readily forms hydrogen bonds with water molecules, conferring excellent anti-freeze and water retention properties to the hydrogel. Even after being stored at −20 °C for 15 days, the hydrogel's mechanical properties and electrical conductivity remain stable. Further, by incorporating ILs into the polymer network backbone, the hydrogel achieves ultra-high conductivity sensitivity, retaining a gauge factor of 9.18 (or 96 %) after storage at −20 °C. Aside from its excellent adhesion and elongation characteristics, the hydrogel exhibits excellent characteristics that enable it to adhere firmly to surfaces as well as detect subtle deformations, such as the bending of a human joint, with ease. Due to its frost-resistant and sensitive properties, this organic ionic hydrogel can be utilized to design wearable sensors that are tailored for monitoring the health of individuals in sub-zero temperatures.