Multilayer alkoxysilane silylation of oxide surfaces

Anhydrous silylation of vinyltrimethoxysilane (VTMS) onto silica and zircon ia substrates was investigated experimentally to demonstrate and quantify t he effects of surface water on multilayer silylation. Silylation coverage w as controlled by the availability of surface water, which is consumed in mu ltilayer silylation reactions. Silylation coverage increased with surface w ater coverage, reaching a maximum at approximately two monolayers of water. The subsequent decline in silylation coverage is attributed to the formati on of bulk polysilanes and the decreased accessibility of the water-bearing surface to the hydrophobic VTMS molecules. Atomic force microscopy images revealed a nanometer-scale clusterlike surface morphology consistent with t he formation of bonded polysilanes. The present study suggests that multila yered silylated surfaces can be prepared reproducibly. Such surfaces could prove useful in applications that require a high concentration of surface a ctive groups such as in ceramic membrane modification, construction of bioc ompatible surfaces, and adhesion enhancement in polymer composites.