Bonding Mechanism of Cyanoacrylates on SiO2 and Au: Spectroscopic Studies of the Interface

Cyanoacrylates form a highly reactive class of adhesives that provide significant adhesive strength to surfaces within a few seconds. Despite their commercial use, the exact bonding mechanism is virtually unknown. In the present work, we spin coat nanometer-thin films of ethyl cyanoacrylate on two model substrates: gold and silicon dioxide. This allows the interface to be studied directly with X-ray photoelectron spectroscopy (XPS). Thus, investigations are feasible to identify chemical interactions at the boundary between the adhesive and metal (oxide), which are possible reasons for film adhesion on the macroscopic scale. On SiO2, an increase in the binding energy of the O═C–O group was observed in thin films, indicating hydrogen bonding with the oxide surface. Metastable induced electron spectroscopy measurements consistently indicate a preferential orientation of the carbonyl group toward the silicon dioxide surface. Furthermore, evidence for an ionic interaction of the adhesive via a carboxylate ion (COO–) with the SiO2 substrate was found by XPS. On gold, on the other hand, neither evidence of an ionic interaction nor evidence of hydrogen bonding could be found.