MODIFICATION OF THE SILICA SURFACE WITH AMINOSILANES

The liquid-phase silylation of silica with various silanes is discusse d. In each case, the reaction mechanism involved is more complex than often believed. Many reactions can occur simultaneously and the result ing surface layer depends largely on the synthesis conditions. Special attention should be given to the role of water in the synthesis. It c an occur as physisorbed molecules on the substrate prior to modificati on, but it may be involved in the reaction mixture itself or even as h umidity during the post-reaction curing step. In each case, the water molecules have an enormous impact on the modification reactions, causi ng a polymerization of the silane molecules and resulting in a thick b ut irreproducible and irregular surface layer.