Liquid metal-enhanced self-healing dual-hard-phase cross-linked waterborne polyurethane for flexible sensors

Flexible strain sensors are increasingly recognized in areas such as health monitoring, mechanical operations, and infrastructure due to their ability to detect minute mechanical signals and conform to irregular surfaces. As sophisticated smart materials, these sensors demand exceptional sensitivity, durability, and robust self-healing capabilities. In this paper, methyl 2,6-dihydroxybenzoate and 2,2′-diaminodiphenyl disulfide were introduced into waterborne polyurethane to form a dual-hard-phase crosslinked matrix, which is characterized by dynamic covalent disulfide bonds and reversible hydrogen bonds. The resultant WPU-D5B2 material exhibits outstanding tensile strength (34.80 MPa) and toughness (190.5 MJ m−3), with a 97.4 % degree of self-healing at 50 ℃ for 2 h. Remarkably, this material maintains 83 % of its original mechanical performance even following recycling processe. This method significantly enhances the performance of flexible strain sensors in complex environments. Consequently, a composite conductor was prepared by blending self-healing waterborne polyurethane (WPU), graphene oxide (GO), and liquid metal (LM). Graphene oxide formed an efficient electronic conductive network, while liquid metal served as a conductive medium, filling microgaps to maintain the integrity of the electron pathway. This innovative dual-conductive mechanism ensures reliable performance in applications such as advanced flexible sensors.