Interfacial Bonding Mechanism of Ethyl Cyanoacrylate Adhesive on Diverse Inorganic Surfaces: A Density Functional Theory Study

Cyanoacrylate-based instant adhesives, commonly known as super glues, are widely used across various fields owing to their high adhesive performance and rapid curing. However, the molecular-level understanding of their interfacial bonding mechanism remains limited. In this study, we investigated the adhesion behavior of ethyl cyanoacrylate (ECA) on typical inorganic surfaces such as Au, Cu, Cu₂O, Al₂O₃, and SiO₂ using periodic density functional theory (DFT) calculations. ECA is known to undergo hydrolysis, which converts its ester group into a carboxyl group. We evaluated how this transformation influences its adhesive properties. Prior to hydrolysis, adhesion to the Au surface is only governed by dispersion interactions, whereas on the other surfaces, the cyano and/or ester groups form charge-transfer interactions, contributing to stronger adhesion. We further explored the hydrolysis mechanism using a reaction path search method, which showed that the reaction proceeds rapidly in the presence of two water molecules and a proton. After hydrolysis, adhesion on Au and Cu surfaces remained largely unchanged. In contrast, adhesion strength significantly increased on Cu₂O, Al₂O₃, and SiO₂, mainly due to enhanced charge-transfer with the surface by the carboxyl and cyano groups of the hydrolyzed ECA. Notably, a barrierless proton transfer was observed on the Cu₂O surface, leading to a substantial increase in adhesion strength. These findings provide molecular-level insights into interfacial interactions in ECA-adhesive systems and offer valuable guidance for designing next-generation instant adhesives.