A one-step aqueous route to prepare polyacrylonitrile-based hydrogels with excellent ionic conductivity and extreme low temperature tolerance†
Generally, polyacrylonitrile (PAN)-based hydrogels possessing excellent mechanical properties are prepared by water replacement after the copolymerization of acrylonitrile (AN) and other hydrophilic monomers in their good organic solvents. However, PAN-based hydrogels synthesized by the conventional strategy not only cause huge environmental problems but also inevitably lose their pristine mechanical properties at subzero temperatures, which severely limits their real-world applications. Here, we designed a novel PAN-based hydrogel under an aqueous system containing ZnCl2 salts without any toxic organic solvents. Based on the salt used in the polymerization strategy, P(AN-co-AMPS) hydrogels (AAHs) can be realized by direct co-polymerization of AN and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) in water in the presence of ZnCl2 salts. ZnCl2 serves three predominant functions: dissolving AN in water to conduct polymerization, inhibiting the formation of ice crystals to realize freeze-tolerance under extremely cold conditions and introducing free ions to promote the conductivity of the hydrogel. Consequently, the AAH simultaneously possesses long-term stability, excellent anti-freezing properties and a high conductivity of 1.16 S m−1 even at −50 °C. Moreover, we demonstrated the AAH as a wearable strain sensor, which features outstanding performance for monitoring different daily human activities in real time. This one-step aqueous-based approach for preparing anti-freezing and conductive PAN-based hydrogels may open a new avenue for the reliable construction of high-performance flexible sensors under environmentally friendly conditions.