Fast Healing of Covalently Cross-Linked Polymeric Hydrogels by Interfacially Ignited Fast Gelation

We report a new design concept that utilizes the Ag+/Fe3+-catalyzed fast gelation of acrylic acid (AA) or AA/comonomer aqueous solutions (e.g., 56 s for the gelation of the 20 wt % AA solution) to achieve fast healing of covalently cross-linked polymer hydrogels. The fast-generated poly(acrylic acid) (PAA) or AA copolymer hydrogel with a covalent network is highly active for the interfacially igniting gelation (IIG) of AA or the AA/comonomer in water through a frontal polymerization process. Using the AA or AA/comonomer aqueous solution as the “repairing liquid,” the fast-generated hydrogels (polymer concentration of 20 wt %) are repeatedly healed at room temperature through the IIG reaction without extra energy input. This IIG reaction-mediated healing (IIG-healing) has healing efficiencies higher than 90%. The healing time can be shortened from ∼60 min to only ∼1 min by increasing the solid concentration of the fast-generated hydrogel to 92 wt %. The IIG reaction also enabled the coating of a hydrophobic polymer layer on the hydrogel, resulting in higher tensile strength, toughness, and much better water retention capacity. We expect that this Ag+/Fe3+-catalyzed fast gelation strategy will pave a facile and energy-efficient pathway to fabricate versatile and multifunctional healing polymers.