Effect of solvent nature on the interaction of γ -glycidoxy propyl trimethoxy silane on oxidised aluminium surface: A study by solution chemistry and surface analysis

A study of the effect of methanol solution composition (in terms of methanol and water proportions) on the hydrolysis of γ -glycidoxy propyl trimethoxy silane (GPS) was conducted using proton nuclear magnetic resonance ( H 1 NMR). In conjunction with this study, adsorption experiments were performed with the same solutions and the films deposited on aluminium surfaces studied by both X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (ToF-SIMS). Hydrolysis experiments were performed until completion of the hydrolysis reaction and it is shown that the addition of methanol to an aqueous silane solution prevents hydrolysis and slows down the hydrolysis kinetics dramatically when added at a proportion of 90% (v/v). The use of a pure methanolic solution, however, stops the reaction totally. XPS data also indicated that adsorption from a solution containing methanol is less favourable than in pure water. An unexpected “inversion” of the adsorption isotherm plateaux obtained for solutions containing 10% and 90% methanol, respectively, as well as with the variation of the fragment ions characteristic of the silane epoxy and silicon atom suggest a variation in the adsorption conformation. A correlation was obtained between the state of hydrolysis deduced from both NMR data and ToF-SIMS intensities of specific fragments. This indicates that the concentrations in solution and the amount adsorbed are either correlated or anti-correlated according to the molecule under consideration. These correlations are more convincing when fragments characteristic of no hydrolysis or with one silanol are considered.