Surface chemical and thermodynamic properties of γ-glycidoxy-propyltrimethoxysilane-treated alumina:: an XPS and IGC study

Alumina and hydrated alumina were treated with hydrolysed gamma -glycidoxypropyltrimethoxysilane (GPS) in aqueous solution. The powder was then dried at various temperatures ranging from room temperature to 120 degreesC. It was found that the hydration treatment used to create hydroxyl sites was efficient in terms of GPS adsorption. The uptake of GPS was determined by quantitative XPS analysis and the hydrated powders exhibited the highest uptake for all drying temperatures except room temperature. Experiments indicated that it was more favourable to use a hydrated powder that had been dried within the temperature range of 50 to 93 degreesC to obtain the highest uptake. IGC measurements indicated no variation of the basicity of the specimens examined and little variation of the surface energy. Nevertheless, modification of the acidity was obtained, with the lowest values between 50 and 80 degreesC drying temperature. Further examination of the C1s XPS signal by peak-fitting of GPS treated powders showed a variation in the type of polar carbons with the treatment temperature. On the basis of the thermodynamic properties and XPS data, two types of interactions between the hydrolysed GPS molecule and the alumina surface are proposed and are correlated with the corresponding temperature. An increase in temperature may lead to opening of the epoxy ring with a subsequent interaction of the silane via this side of the molecule. This mechanism occurs jointly with the classical type of interaction expected of silanes via the silanol group. It is thought that the former is favoured at high temperature if the GPS film is not damaged. It is also shown that the epoxy functionality is not hydrolysed during hydrolysis of GPS in the aqueous solution.