The nature of the hydrophobic layer in hybrid nanomaterials

Hydrophobic modification of titania surfaces have been attracting increasing attention. Such interest was initiated by the fundamental importance of wetting phenomena in various technological applications, such as self-cleaning processes, the prevention of clotting in artificial blood vessels, or the protection of outdoor cultural heritage. Notwithstanding the great interest and the manifold applications, the attachment of hydrophobizing molecules at TiO2 surfaces still remains poorly understood at the molecular level and hardly discussed in the literature. In this work the attachment of trifunctional siloxanes, both commercial and prepared in laboratory on TiO2 nanoparticles is investigated, concerning both the applicative aspects of wettability and self-cleaning properties and also the more fundamental features of bonding and structure of the surface layers. Contact angle measurements as a function of the siloxane oxide coverage are performed together with self-cleaning tests. The role played by siloxanes on the oxide surface area and porosity are analyzed. The structure of the surface layer and the modes of attachment of Si atoms are investigated by combining data of CP/MAS NMR with ATR-FTIR analyses.