ADSORPTION BEHAVIOR OF A SILANE COUPLING AGENT ON COLLOIDAL SILICA STUDIED BY GEL-PERMEATION CHROMATOGRAPHY

The adsorption behavior of a silane coupling agent deposited onto silica is examined as a function of both drying time and silane concentration using gel permeation chromatography (GPC). Information concerning the bonding of the silane to the surface, the amount adsorbed, and the molecular species present is obtained from GPC by measuring the extractable, physisorbed silane. Chemisorption occurs rapidly within 1 day, and continues to gradually increase until 14 days. Fourier transform-infrared diffuse reflectance spectroscopy (DRIFT) is used to obtain information concerning the adsorption behavior of the chemisorbed silane. The effect of surface coverage on the orientation of silane molecules has been studied. The effect of acid on the adsorption behavior is investigated as a function of concentration of acid. Addition of hydrochloric acid increases the molecular weight of the adsorbed silane species. The molecular species chemisorbed on the silica surface is different with different concentrations of hydrochloric acid, and strongly affects the adsorption behavior. Higher-molecular-weight species of silane molecules reduce the maximum amount of chemisorbed silane. In addition, the non-hydrogen-bonded carbonyl component increases with increasing concentration of hydrochloric acid. © 1991 Academic Press, Inc. All rights reserved.