Hybrid dual crosslinked polyacrylic acid hydrogels with ultrahigh mechanical strength, toughness and self-healing properties via soaking salt solution

Abstract

Broader applications of polymer hydrogels are largely constrained by their poor mechanical performance. Here, we report our strategy of achieving ultrahigh mechanical strength, toughness, and self-healing properties simultaneously in a hybrid dual crosslinked polyacrylic acid (PAAc) hydrogel. The hybrid PAAc hydrogel was fabricated in a one-pot reaction with two types of crosslinking points, i.e. the primary chemical cross-linkers that create covalent cross-linking among PAA chains and the secondary physical cross-linkers Fe3+ that introduce ionic coordinates between Fe3+ and −COO− groups. The resulting hybrid PAA hydrogel was subsequently subject to a simple saline solution soaking to become highly mechanically robust as a result of chain entanglement within the network. Favorable mechanical properties possessed by such hybrid hydrogels included high tensile strength (ca. 1.794 MPa), large elongation at break (ca. 13.209 times), and excellent work of extension (ca. 11.475 MJ m−3). In addition, the hydrogels exhibited self-healing properties because of their inter-chain interactions at ambient conditions (tensile strength can recover approximately 30% of the initial after self-healing for 48 h from a cut-off state). This work demonstrates a simple and promising strategy of preparation of novel ductile and doughty hydrogels through dual crosslinking and saline solution soaking.