CO₂-switchable self-healing of ionic liquids-based hydrogels

High-performance soft materials with stimulus-responsive and self-healing properties have received a lot of attention in modern environmental and energy technologies. However, it was difficult to construct supramolecular hydrogels integrating different functionalities. In this work, we reported a novel class of supramolecular hydrogels made of ionic liquids (ILs) with CO₂-responsive and self-healing properties. These ILs were found to form hydrogels with H₂O. Upon bubbling with CO₂, the transparent and stable IL-based hydrogels transformed into sols, which returned to their initial gel state after bubbling with N₂ at 65°C. The reversible gel-sol phase transformation behavior was demonstrated by rheological, polarizing, scanning and cryogenic transmission electron microscopy measurements. Spectroscopic studies indicated that the mechanism of gel-sol transition was attributed to reversible reaction between the anions of the ILs and CO₂ in the hydrogel, which destroyed the hydrogen bonding between the anions and water. Self-healing ability of the hydrogels was confirmed by rheological measurements. The self-healing mechanism was ascribed to the disruption and reconstruction of hydrogen bonds in IL-based hydrogels using temperature-dependent Fourier transform infrared spectroscopy. The CO₂-responsive and self-healing ability make these novel hydrogels attractive in smart soft materials.