The interaction of alkoxy silane coupling agents with silica surfaces

Abstract The interactions of γ‐aminopropyltriethoxy silane (A‐1100), γ‐methacryloxytrimethoxy silane (A‐174), γ‐glycidoxytrimethoxy silane (A‐187), and ethyltriethoxy silane (A‐15) with silica surfaces have been studied by means of infrared spectroscopy. The results indicate that the major force holding the silane to the silica surface after application from dilute solutions is primary chemical bonding. These bonds are formed by a condensation reaction between silanols on the hydrolyzed form of the silane and hydroxyl groups on the silica surface. In the case of the amino‐silane (A‐1100), hydrogen bonding was found to exist but was of minor importance in bonding the silane to the surface. In studying the effects of the addition of water, acetic acid, or n‐propylamine to various silane treating solutions, it was found that n‐propylamine has a unique catalytic effect on the condensation reaction. This catalytic effect explains the observation that γ‐aminopropyltriethoxy silane is more reactive than the other silanes studied. It is felt that silanes not containing an amine group can be made more effective if they are applied in the presence of an amine catalyst.