UV-induced superlubricity

Un article de Surface du verre et interfaces.

Ramzi Jribi(PhD 2005-2008), Muriel Beauvais, Etienne Barthel, Davy Dalmas & Elin Sondergard

Photo-induced redox reactions of adsorbed organic substances on TiO₂ based materials in air or liquids have been extensively studied since the 1970s. These photochemical phenomena induced by UV light irradiation are used for water photoelectrolysis or waste water and air purification. The discovery of a reversible UV induced hydrophilic conversion of TiO₂ surfaces in 1995 widened their use in self-cleaning, anti-fogging and antibacterial applications.

Several studies using atomic force microscopy (AFM) in Lateral Force Microscope (LFM) mode report that the macroscopic hydrophilic conversion of TiO₂layers in ambient air is also accompanied by a photo-induced friction force variation at nanoscale. Results highlight the correlation between capillary forces and friction as well as their dependence on the surface wettability in ambient air, but they can’t explain why TiO₂ based materials prevent mineral contamination in outdoor use. When exposed to rain, TiO₂ films are subjected to a relative humidity close to 100% and the contact between particles and TiO₂ surfaces can be considered to be immersed in water, resulting in the suppression of liquid-mediated capillary forces.

However, on the basis of our previous results, a question relates to the ability of mineral contaminants to slide on TiO₂ layers when particles experience Van der Waals attraction forces or short-range repulsive forces.

Our work focuses on the impact of the surface forces modification between TiO₂ layers and silica contaminants on the sliding resistance of the particles.The friction force between a colloidal probe and polycrystalline Anatase TiO₂ films is measured in water by using AFM in LFM mode, when the layers are adhesive and non-adhesive.