Novel Multifunction Epoxy Thermoset Designed by Manipulating the Silicon-Oxidation Flexible-Rigid Network Topology: Toughening, Strengthening, and Acid/Alkali Resistance

The inherent strength–toughness trade-off in thermosetting epoxy resins (EPs) renders them susceptible to permanent failure from crack propagation during use, impeding their sustainable development. This study presents a topology-based approach for constructing and regulating the cross-linked network that couples hardness with softness at the molecular level to solve the strength–toughness trade-off. Specifically, an organosilicon compound with an aliphatic chain (KH560) and an organosilicon compound with only short side groups (tetraethoxysilane) are used to introduce rigid and flexible structures that work synergistically into EP. By adjusting the proportion of rigid (i.e., rigid units of EP and cross-linked Si–O–Si structures) and flexible structures (i.e., linear Si–O–Si structures and aliphatic chains), the size and concentration of the network free volume as well as network topological secondary structures, including the molecular weight of the resin, chain flexibility, and cross-linking density, can be regulated. Furthermore, the effects of the network free volume and network topological structure on performance are studied. The performance of EP can be controlled, and strength–toughness trade-off in EP can be overcome. For example, the tensile strength and critical strain energy release rate of modified EP (ESi-D1) are 47 and 444% higher than those of conventional EP, respectively. This study provides an efficient method to construct a network topology that controllably couples hardness with softness and overcomes the strength–toughness trade-off, improving the performance beyond traditional paradigms and opening new applications for EP.