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

Alumina and hydrated alumina were treated with hydrolysed gamma -glycidoxyp ropyltrimethoxysilane (GPS) in aqueous solution. The powder was then dried at various temperatures ranging from room temperature to 120 degreesC. It w as found that the hydration treatment used to create hydroxyl sites was eff icient in terms of GPS adsorption. The uptake of GPS was determined by quan titative 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 w ithin the temperature range of 50 to 93 degreesC to obtain the highest upta ke. IGC measurements indicated no variation of the basicity of the specimen s examined and little variation of the surface energy. Nevertheless, modifi cation of the acidity was obtained, with the lowest values between 50 and 8 0 degreesC drying temperature. Further examination of the C1s XPS signal by peak-fitting of GPS treated powders showed a variation in the type of pola r 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 t he corresponding temperature. An increase in temperature may lead to openin g of the epoxy ring with a subsequent interaction of the silane via this si de of the molecule. This mechanism occurs jointly with the classical type o f 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 hyd rolysis of GPS in the aqueous solution.