Roughness influence on the attachment modes of siloxanes on TiO2 surfaces

The modulation of TiO2 surface properties represents a hot topic in several fields, from biomaterials to photovoltaics, from chemical sensors to microelectronics. These applications show the necessity of a better theoretical comprehension of the role of micro and nanometric roughness in the tailoring of the wettability of this kind of surfaces. Here, we evaluate how different roughness degrees of the TiO2 substrate influence its interaction with functionalizing molecules in siloxanes-TiO2 composites. A sol-gel based procedure is developed for the deposition of smooth and transparent TiO2 layers (rms < 1 nm for 10 x 10 μm2). The resulting materials are characterized by TGA, FT-IR, dynamic contact angle measurements, SEM and AFM. Rough TiO2 films, instead, are obtained from different procedures, such as spin-coating of sol-gel TiO2 nanoparticles. Both smooth and rough films are used as substrates for the chemical vapor deposition of different siloxanes. The composite layers are characterized by AFM, FT-IR, and dynamic contact angle with different solvents. Moreover, the interaction between siloxane molecules and the TiO2 surface is studied by means of CP/MAS NMR and compared to SiO2 substrates, showing the peculiarity of the attachment mode of the siloxane molecules in the two cases.