Enhanced hydrolytic stability of siliceous surfaces modified with pendant dipodal silanes

Abstract

Dipodal silanes possess two silicon atoms that can covalently bond to a surface. They offer a distinct advantage over conventional silanes commonly used for surface modification in terms of maintaining the integrity of surface coatings, adhesive primers, and composites in aqueous environments. New nonfunctional and functional dipodal silanes with structures containing "pendant" rather than "bridged" organofunctionality are introduced. The stability of surfaces in aqueous environments prepared from dipodal silanes with hydrophobic alkyl functionality is compared to the stability of similar surfaces prepared from the conventional silanes. In strongly acidic and brine environments, surfaces modified with dipodal silanes demonstrate markedly improved resistance to hydrolysis compared to surfaces prepared from conventional silanes. Pendant dipodal silanes exhibit greater stability than bridged dipodal silanes. The apparent equilibrium constant for the formation of silanol species by the hydrolysis of a disiloxane bond was determined as Kc=[SiOH]2/[Si-O-Si][H2O]= 6±1×10-5 and is helpful in understanding the enhanced hydrolytic stability of surfaces modified with dipodal silanes. Two feet are better than one! Nonfunctional and functional dipodal silanes with structures containing "pendant" rather than "bridged" organofunctionality were synthesized. Surfaces modified with pendant dipodal silanes were found to be more resistant to hydrolysis than the bridged structure with single-carbon separated (disilapropyl)silanes, demonstrating the greatest resistance to hydrolysis and best stability (see figure). © 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of Creative Commons Attribution NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.