Interplay between Chemistry and Texture in Hydrophobic TiO2 Hybrids

Organic-nano-TiO2 hybrids are successfully employed in different fields, from biomaterials to self-cleaning processes and from sensing to photovoltaics. The specific wetting properties of these materials bear relevance to any application. Here, nano-TiO2 films with a multiscale roughness, as shown by AFM, are derivatized with tri- and bifunctional siloxanes, bearing either alkyl or aromatic end groups. Dynamic contact angle measurements show a marked dependence of the wettability on the siloxane nature, leading to different self-cleaning properties, as assessed by ATR-FTIR. The different behavior is rationalized on the grounds of the structure of the functionalized layer, by employing solid state Si-29 CP-MAS NMR and EDX mapping. Semiempirical calculations of hybrids dipole moments in conjunction with solvent surface energy components allow us to explain the strongly different solvents wettability. This work brings attention to the importance of the hydrophobizing molecule nature and its chemical interactions for the interpretation of wettability versus surface texture.