D. J. Ondrus, F. J. Boerio
Jul 1, 1988
Journal of Colloid and Interface Science
Abstract Infrared spectroscopy was used to determine the effect that metal substrates such as titanium, iron, 1100-series aluminium, 2024 aluminum, and copper have on the molecular structure and properties of γ-aminopropyltriethoxysilane (γ-APS) primer films. When γ-APS was adsorbed onto any of the substrates from aqueous solutions at pH 10.4 for 1 min and then dried at room temperature for 30 min, the molecular structure of the primer films was similar and consisted for low-molecular-weight siloxane polymers containing a considerable amount of absorbed carbon dioxide in the form of amine bicarbonates. After the films were dried at elevated temperatures, the structures differed significantly. When drying was carried out at 110°C, films formed on titanium, iron, and 1100-series aluminum were similar. The extent of polymerization in the films increased and most of the bicarbonates were dissociated. However, the amino groups in films formed on 2024 aluminum and copper oxidized to imine groups and the polymerization did not increase significantly. After drying at 150°C, the films formed on titanium, iron, and 2024 aluminum were all oxidized to the imine but films on 1100-series aluminum were not, suggesting that the oxide on 1100-series aluminum inhibited the free radical oxidation reaction. Dissociation of the bicarbonates and oxidation of the amino groups were important factors in the reaction of the primers with epoxy resins. The reaction of primer films on iron and 2024 aluminum with epoxy resins at 75°C was slow because the temperature was too low for dissociation of the bicarbonates to occur. At 150°C, epoxies reacted readily with γ-APS films on iron but not with those on 2024 aluminum. For primer films on 2024 aluminum, the preferred reaction at 150°C was oxidation of the amino groups.