Multiscale Rough Titania Films with Patterned Hydrophobic/Oleophobic Features

Abstract

Oxide-based hybrids are promising systems to modulate the surface properties and impart different functionalities. Here, the wettability features of rough titanium dioxide (TiO2) layers derivatized by siloxanes are tailored with respect to both water and nonaqueous solvents. The adopted synthetic procedure is very simple and may be extended to different substrates, as it is based on the direct functionalization of homemade, tailored, TiO2 nanoparticles by different siloxanes, both fluorinated and nonfluorinated. Nanotitania provides a multiscale roughness able to impart superhydrophobicity and its photocatalytic activity can be exploited to obtain surfaces with patterned wettability by photocatalytic lithography. The behavior of the different siloxanes (oleophobicity degree, self-cleaning properties, and kinetics of ultraviolet degradation) is related to the surface energy components of the bare siloxane films, evaluated by Owens–Wendt classical model, and to the structure of the siloxane monolayer at the TiO2 surface, as determined by 13C and 29Si solid-state nuclear magnetic resonance. Finally, patterned structures with tunable hydrophobic and oleophobic patches are obtained by using the photocatalytic activity of the oxide. The siloxane photodegradation process is analyzed by Fourier transform infrared spectroscopy. The resulting wetting contrast is exploited to obtain a site selective adsorption of a dye molecule. The presented procedure can be applied to obtain the site selective deposition or growth of a large variety of materials, such as semiconductor quantum dots, polymers, or biological molecules.