Frost-Resistant Ionic Conductive Hydrogels toward Sensor Application

Conductive hydrogels have gained significant attention in flexible electronic products due to their excellent flexibility, conductivity, and stimulus responsiveness. However, the high water content in conventional hydrogels inevitably leads to icing at low temperatures, severely hindering their application. To address this issue, frost-resistant ionic conductive hydrogels (AA-Xα) based on polyionic liquids (PILs) were prepared using vinyl choline-amino acid ionic liquids (Cho-AA-VILs), acrylamide (AAm), and octadecyl methacrylate (C18) as the reactive monomers through micellar polymerization. At the same time, antifreezers including different inorganic salts and organic solvents were introduced into the hydrogel network to further improve the antifreezing properties of AA-Xα hydrogels. The effects of antifreeze types and amounts on the performance of AA-Xα antifreezing hydrogels were systematically investigated. The results showed that the introduction of magnesium salts endowed AA-Xα antifreezing hydrogels with higher frost resistance than that of lithium and aluminum salts. Meanwhile, AA-Xα antifreezing hydrogels displayed the strongest tensile properties and electrical conductivity at −20 °C when the concentrations of inorganic salts were 0.5 mol·L–1 and 2 mol·L–1, respectively. In addition, the introduction of glycerol also led to a significant improvement in the antifreezing properties of AA-Xα antifreezing hydrogels. Furthermore, the AA-Xα antifreezing hydrogels exhibited sensitive, rapid, and stable sensing properties at −20 °C. Importantly, the AA-Xα antifreezing hydrogels could be used to detect various physiological activities and changes of microexpressions in the human body at low temperatures. These results indicated that AA-Xα antifreezing hydrogels had tremendous potential for intelligent and flexible electronic device applications.