TiO2–SiO2 composite thin films have been deposited via a sol–gel route. Their morphological, physico-chemical, and wettability properties have been studied. It is shown that composite films exhibit an unexpected natural super-hydrophilicity that persists with time in the absence of any UV light exposure. Depending on the experimental conditions, this natural super-hydrophilicity can persist for at least eight weeks in ambient aging conditions. Such a property allows envisaging applications to surfaces with enhanced cleanability in atmospheres where UV light is not permanently present. It is shown that natural carbon contamination does not preponderantly influence the persistent super-hydrophilicity of TiO2–SiO2 composite films. This property is then studied and discussed with respect to the film morphological and physico-chemical properties.

Ellipsometry porosimetry (EP) is an emerging technique that is well adapted to porous thin films analysis; it is non contact and non destructive. EP tools developed at SOPRA, allows us to obtain adsorption isotherms with many different adsorptives at an ambient temperature. EP leads to the same results as classical adsorption experiments (e.g. porosity, pore size distribution …), but it also has some particular features leading to new information. For instance, our optical setup (Spectroscopic Ellipsometry) allows us to determine the variation of the thickness of the samples during the adsorption experiment. It is also very sensitive to interfaces; it is thus possible to detect a porosity gradient or to study a bi-layer sample and plot the two corresponding adsorption isotherms at the same time (Bourgeois et al. 2004). For porous thin films with a non porous barrier layer deposited on top, it is also possible to study the lateral diffusion phenomenon in the film (see figure below). In this paper, we will demonstrate a part of the different features of EP for adsorption on porous thin films.

Spectroscopic ellipsometry is the technique of choice to characterize thickness and refractive indices of transparent and semi-transparent thin layers with thickness ranging from few Angstroms to few micrometers. However, in case of porous thin film, traditional EMA (Effective Medium Approximation) fails to provide qualitative information on porosity. However, Spectroscopic Ellipsometry can benefit elaborated hardware and software set-up involving the adsorption/desorption of an adsorbate in the porous thin film, we call it, Ellipsometry Porosimetry Atmospheric (EPA) and the adsorbate is water. The change in refractive index induced by the introduction of water is measured and thanks to Lorentz Lorenz effective medium model, the volume of water adsorbed by the material is calculated. EPA becomes an effective method for characterization of porosity volume, pore size distribution (PSD), average pore size, cumulative surface area and Young's modulus of porous films. EPA is also suitable to evaluate the sealing of a porous layer. An example of study is carried on for TiO2 mesoporous prepared by Evaporation Induced Self-Assembly with various calcinations treatment. Plots results are characteristic of mesoporous medium with well defined pore dimensions. Upon calcinations, EP-A allows to follow a significant pores enlargement from 3 to 10 nm. In this paper, the instrument as well as TiO2 porous thin film study will be presented.

Previous studies suggest that granular interfaces induce a natural and persistent super-hydrophilicity in TiO2–SiO2 composite thin films deposited by sol–gel route. This effect enables to consider self-cleaning applications that do not require a permanent UV exposure, whereas such a permanent exposure is necessary for pure TiO2 films. In this study, TiO2–SiO2 composite thin films have been deposited from a TiO2 anatase crystalline suspension and different SiO2 polymeric sols. Wettability studies show that a suitable control of the TiO2–SiO2 mixed sol formulations noticeably enhances persistence of the natural super-hydrophilicity in composite films. It is shown that, beside granular interface effects, modifications in the composite film morphologies can noticeably influence wettability properties.