Graphical models of dominant topologies of polymer-substrate adhesive-interfacial strength and toughness

It is a challenge to determine the dominant topological characteristics of mechanical properties of adhesive interfaces. In this paper, we used graph theory and molecular dynamics simulation to investigate the influence of topological characteristics on the strength and toughness of highly cross-linked polymer interface systems. Based on the microstructure of the adhesive system, we extracted the dominant topological characteristics, including the connectivity degree (D) that determines the yield strength, and the average node-path (P) and the simple cycles proportions (R) that determine the deformability and load-bearing capacity during the void propagation respectively, which co-determine the toughness. The influence of the wall-effect on the dominant topological characteristics was also analyzed. The results showed that the interfacial yield strength increases with the increase of D, while the toughness increases with the increase of P and R. The wall-effect has a significant influence on D, P, and R. The strong wall-effect causes the enrichment of amino groups near the wall and insufficient cross-linking away from the wall, leading to the lower D and R, i.e., the lower yield strength and load-bearing capacity during the void propagation. With the attenuation of the wall-effect, the D increases gradually, while the P and the R first increase and then decrease, showing an optimized wall-effect for the toughness of the adhesive interface. This paper reveals the dominant topological characteristics of adhesive interfacial strength and toughness, providing a new way to modulate the mechanical properties of polymer adhesive interface systems.