Titanium dioxide (TiO₂) plays a crucial role for modern technical applications such as the design of new catalysts or biomaterials. TiO₂ particles in the modifications of rutile or anatase are a widely used material as an inorganic white pigment. In particle processing the force interactions within particle collectives are of outmost interest in terms of bulk flow properties and agglomerate dispersibility. As the adhesion between small particles is mostly driven by capillarity- and van der Waals forces, the investigation of surface chemistry plays a crucial role to understand interactions at TiO₂ particle surfaces. For studies of particle ensembles a new experimental setup was developed to investigate particle parameters under both control of relative humidity (capillary forces) and UV light exposure (hydrophobic to hydrophilic transition). By combined Fourier Transform Infrared Spectroscopy (FTIR) and quartz crystal microbalance (QCM) we studied the influence of surface hydroxyl densities and molecular adsorbates on the formation of surface water adsorbate films in environments of defined relative humidity.

To study the formation of adsorbates on a model surface, TiO₂(100) and TiO₂(110) single crystalline surfaces were prepared by a wet chemical etching procedure followed by an annealing step. The crystal surface and the native adsorbate layer were studied by means of angle resolved photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and atomic force microscopy (AFM).

The surface analysis by AFM and LEED revealed a single crystalline TiO₂ surface for both crystal orientations. An ad-layer of surface-hydroxides and specifically adsorbed water additionally to the native contamination layer of low-weight (hydro)carbon species formed under ambient conditions could be proven by angle resolved XPS experiments.

As a model of the carboxy-functional, (hydro)carbon contamination film the adsorption of nonadecylcarboxylic acid (NDCA) on the crystal surface was studied by AFM and angle resolved XPS experiments. Here a significantly different mechanism of adsorption was found comparing the TiO₂(100) and TiO₂(110) surfaces. AFM investigations showed a micellar adsorption of NDCA on the (100) surface forming a dense layer of NDCA micelles which could be removed from the surface by AFM based “nanoshaving”-experiments. In comparison the (110) surface showed very weak interactions with NDCA leading to a coverage of less than one monolayer as a result of different surface termination in comparison to the (100) crystal.