Molecular dynamics simulations of surface welding in crosslinked networks with thermally reversible linkages
YG Sun and H Yang and WJ Xia and YF Guo, APPLIED SURFACE SCIENCE, 527, 146947 (2020).
Crosslinked networks with thermally reversible linkages, e.g. Diels- Alder networks, undergo depolymerization at elevated temperatures and polymerization at relative low temperatures. This depolymerization, repolymerization sequence enables network rearrangement, which can result in intriguing properties cannot be achieved in conventional thermosetting polymers, such as surface welding. In this study, we establish a molecular dynamics computational approach involving the depolymerization, repolymerization reaction sequence to investigate the surface welding process of Diels-Alder networks. In this approach, two separate crosslinked Diels-Alder networks are brought in contact to allow depolymerization and interdiffusion at elevated temperatures, as well as subsequent repolymerization and interfacial linkages formation at relative low temperatures. The extent of depolymerization is correlated to temperature utilizing the van't Hoff equation. The influences of welding temperature and welding time on the interfacial structure are investigated by analyzing the interfacial linkages distribution, interpenetration depth, and minimal path length. The mechanical responses of interfaces welded under different conditions are further discussed. Our results show that when the welding temperature is below the gel-point temperature, increasing welding time shortens the minimal path length and reduces the extensibility of the welded interface. The interfacial strength can reach the bulk value with increasing welding time when the welding temperature is above the gel- point temperature. This study provides insights into the molecular mechanisms that govern the mechanical responses of welded Diels-Alder networks and can be helpful to guide the selections of suitable welding conditions.
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