Zwitterionic Osmolyte-Based Hydrogels with Antifreezing Property, High Conductivity, and Stable Flexibility at Subzero Temperature

Conductive hydrogels have emerged as fascinating materials applied in flexible electronics because of their integrated conductivity and mechanical flexibility. However, the large amounts of water in conductive hydrogels inevitably freeze at subzero temperature, causing a reduction of their ionic transport ability and elasticity. Herein, the bioinspired antifreezing agents-zwitterionic osmolytes (e.g., betaine, proline) are first proposed to prevent ammonium chloride-containing Ca-alginate/polyacrylamide hydrogels from freezing. With a facile one-pot solvent displacement method, the zwitterionic osmolytes can displace the water molecules inside the hydrogels. Due to the excellent freeze tolerance of zwitterionic osmolytes, the resulting zwitterionic osmolyte-based hydrogels exhibit outstanding ionic conductivity (up to approximate to 2.7 S m(-1)) at -40 degrees C, which exceeds the conductivities of most reported conductive hydrogels. Meanwhile, they present stable mechanical flexibility over a wide temperature range (-40 to 25 degrees C). More importantly, two types of the resulting hydrogel-based flexible electronics, including a capacitive sensor and a resistive sensor, can maintain their response function at -40 degrees C. This work offers a new solution to fabricate conductive hydrogels with antifreezing ability, which can broaden the working temperature range of flexible electronics.