HYDROLYTIC DAMAGE STUDY OF THE SILANE COUPLING REGION IN COATED SILICA MICROFIBERS. pH AND COATING TYPE EFFECTS

摘要

Aqueous solutions of three silanes to cover silica microfibers were used, being the 3-aminopropyltriethoxysilane (APTES) and the 2-aminopropylmethyldiethoxysilane (APDES) the reagents for preparing them at the proportion of (APTES/APDES): 1/0; 1/1 and 0/1. The pyrene sulfonyl chloride fluorescent moiety (PSC) was chemically attached to the silanized substrate via the sulfonamide 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 microfibers composite materials occurs under an equilibrium process. It was obtained the activation energies (Ea) for the hydrolytic damage considering the rate to reach the equilibrium. The values of Ea 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{sub}(silane)-O-Si{sub}(silane) while the OH{sup}- groups were thought to catalyse the reaction.