Certain forms of photoactive titanium dioxide (TiO2) can create highly washable surfaces.  The light-induced conversion of relatively hydrophobic to hydrophilic surfaces, especially in the case of TiO2, has been attributed to an increase in surface hydroxyl groups generated during the photochemical conversion processes.  A coated surface is considered wetted if a liquid spreads evenly over the surface without the formation of droplets.  As the photocatalyst surface becomes more hydrophilic, water contact angles will decrease. Coating wettability can be influenced by environmental conditions, such as heat, light intensity and wavelength distribution, and relative humidity.  The hydrophobic/hydrophilic switching of several commercially available and custom photocatalytic thin films were investigated by measuring the water contact angles as a function of UV irradiation time and wavelength. The experimental conditions required to achieve the superhydrophilic state for each photocatalytic coating material and the persistence of this state in the absence of light is discussed.

Super-hydrophobic/hydrophilic switching of photocatalytic titanium dioxide coatings

243rd National Meeting (2012)

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