Role of imperfect coordination of amorphous metal oxide in its chemical reaction with epoxy resin in metal - polymer hybrid material

The chemical bonding between laser - induced metal oxide and polymer highly determines the interfacial bonding performance of metal - polymer hybrid materials. To achieve reliable interfacial chemical bonding, it is crucial to gain a molecular/atomic level understanding of the chemical reaction mechanism between the metal oxide and epoxy resin (main components of epoxy polymer). Previous research has demonstrated that laser ablation induces the formation of amorphous aluminium oxide on aluminium alloy surfaces. Our solid - state nuclear magnetic resonance (ssNMR) investigation reveals that this amorphous aluminium oxide is consisted mainly of 4 - fold and 5 - fold coordinated Al sites. Through an innovative combination of ssNMR and density functional theory calculations, this aluminium oxide was confirmed to form Al - O - C bonds with epoxy resin, preferentially at imperfectly coordinated Al sites due to active donor - acceptor interactions. It is clarified that imperfect coordination of amorphous aluminium oxide plays a more critical role than its amorphous nature in forming stable adsorption structure with epoxy resin. Furthermore, compared to on crystalline surface, 5 - fold coordinated Al site on amorphous surface exhibits higher reactivity, and the origin of activity is revealed through distortion/interaction analysis. This study provides a research guidance for further regulation and optimization of interfacial reactivity and bonding characteristics of metal - polymer hybrid materials.