Hyperbranched Macromolecular Physical Crosslinker-Based Dual Crosslinked-Network Conductive Hydrogel as a Sensitive and Highly Stretchable Strain Sensor with Improved Mechanical Properties

Hydrogels are often limited in their applications due to their inherently weak mechanical properties. In this study, a carboxyl-functionalized hyperbranched polymer (HPEHO-star-PAA) was synthesized and used as a macromolecular physical cross-linker to enhance the mechanical properties of conductive hydrogels. Fe3+–carboxyl complexes were incorporated into the P(AAm-co-AA)/HPEHO-star-PAA hydrogel to form a dual cross-linked network structure. The cross-linker N,N′methylenebis(acrylamide) (MBA) was chemically incorporated into the network to form covalent cross-links, strengthening the network. Meanwhile, the coordination bonds formed between Fe3+ and carboxylate act as dynamic noncovalent cross-links, enhancing the energy dissipation capacity. This study successfully prepared a hydrogel with excellent mechanical properties, including an elongation at break of 573%, a tensile strength of 3.68 MPa, and a toughness of 14.09 MJ/m3. Additionlly, the conductive hydrogels also showed good antiswelling ability due to the strong binding force between Fe3+ and carboxylate. Moreover, P(AAm-co-AA) hydrogels used as strain sensors possessed stability and were highly sensitive. Therefore, this well-designed conductive hydrogel, with high mechanical strength, excellent toughness, good antiswelling ability, and high sensitivity, shows great potential for use in flexible strain sensor applications.