Coadsorption of water and selected aromatic molecules to model the adhesion of epoxy resins on hydrated surfaces of zinc oxide and iron oxide

The coadsorption of heavy water and some aromatic molecules was studied on zinc oxide and iron oxide surfaces by temperature-programmed desorption (TPD) in order to elucidate the role of water at the polymer/oxide interface at a molecular level. Glycidyl 2-methylphenyl ether and 2-phenoxy ethanol were selected as the model compounds of epoxy resins and were used as adsorbates in addition to some simpler substituted benzenes. It was found that on zinc oxide, water was adsorbed coordinatively on zinc sites and the heat of adsorption was 89 kJ/mol while on iron oxide, water was adsorbed physically and the heat of adsorption was 55 kJ/mol. On zinc oxide, the adsorption of benzene, toluene and α,α,α-trifluorotoluene was interfered with water while the adsorption of phenol and the epoxy model compounds was not affected by water. On iron oxide, none of these organic molecules were replaced by water. Based on these findings, it was concluded that the adhesion mechanism of the epoxy resin proposed in the previous paper holds even when the oxide surfaces are covered with water. Namely, the adhesion is due to the chemical bond formed by CO bond dissociation to form surface phenoxy species.