Hydrolytic damage study of the silane coupling region in coated silica microfibres:: pH and coating type effects

Aqueous solutions of three silanes to cover silica microfibres were used, being the 3-aminopropyltriethoxysilane (APTES) and the 3-aminopropylmethyldiethoxysilane (APDES) the reagents for preparing them at the proportion of (APTES/APDES): 1/0, 1/1 and 0/1. The I-pyrene sulphonyl chloride (PSC) fluorescent moiety was chemically attached to the silanised substrate via the sulphonamide formation. The hydrolytic degradation phenomenon of the silane coupling layer was studied as a function of: (i) temperature, (ii) coating layer type and (iii) pH (4, 7 and 10). The hydrolytic damage in the coupling region of the silica microfibres composite materials occurs under an equilibrium process. It was obtained the activation energies (E-a) for the hydrolytic damage considering the rate to reach the equilibrium. The values of E. depended on the type of coating and on the pH. As a consequence, the rate of hydrolytic damage could be related to the proportion of Si-silane-O-Si-silane, while the OH- groups were thought to catalyse the reaction. (C) 2003 Published by Elsevier B.V.