Metal-Coordination Complexes Mediated Physical Hydrogels with High Toughness, Stick–Slip Tearing Behavior, and Good Processability

Abstract

It is challenging to develop hydrogels with a combination of excellent mechanical properties, versatile functions, and good processability. Here we report a physical hydrogel of poly(acrylamide-co-acrylic acid) (P(AAm-co-AAc)) cross-linked by carboxyl–Fe3+ coordination complexes that possesses high stiffness and toughness, fatigue resistance, and stimulation-triggered healing along with shape memory and processing abilities. The copolymers have randomly dispersed AAm and AAc repeat units, making the physical cross-links with different strength. The strong coordination bonds and their associations serve as permanent cross-links, imparting the elasticity, whereas the weak ones reversibly rupture and re-form, dissipating the energy. Furthermore, a stick–slip instability is observed during the tearing test, which should be associated with the specific nature of metal-coordination bonds that are strong yet fragile. Because of the dynamic nature of coordination bonds, both tensile and tearing mechanical propert...