A Conductive, Self-Healing Hybrid Hydrogel with Excellent Water-Retention and Thermal Stability by Introducing Ethylene Glycol as a Crystallization Inhibitor

The rapid development of flexible electronics motivates the design and synthesis of stable hydrogels that possess good stretchability and conductivity under harsh environment. The long-term durability of traditional hydrogels generally fails at high temperatures. In this work, a high-temperature-tolerant, self-healable hybrid hydrogel showing excellent water-locking and adhesive properties was developed through ultraviolet curing of acrylamide (AM) and hyper-branched polyethyleneimine (PEI) in highly salted ethylene glycol-water solution. Ethylene glycol was used as a crystallization inhibitor and greatly enhanced the solubility of sodium acetate (NaAc). The fabricated hydrogel can retain 75 % of its initial weight for 9 hours at 100 °C or 88 % of its initial weight for 77 hours at 15 % relative humidity (RH) environment. The dehydrated gel was flexible (tensile strain > 1700 %) and conductive after storing at high temperatures (e.g. 100 °C) for a long term. Moreover, the highly salted hydrogel showed remarkable water adsorbing ability in the air: it can recover to its original weight after losing water at high temperature or low humidity conditions. In addition, the separated hydrogel fragments could heal into a single piece in 30 s, and the hydrogel showed reversible adhesiveness to both organic (6.2 kPa for pigskin, 28 kPa for wood) and inorganic (111.9 kPa for glass, 135.5 kPa for iron) substances for at least 5 cycles. This work provides a facile way of obtaining multi-functional conductive hydrogels that can work at high temperatures, demonstrating long-term prospects in engineering applications.