Robust and transparent smooth amphi-repellent coating with physical self-cleaning and photocatalytic activities

Smooth amphiphobic and amphi-repellent surfaces have attracted attention because their ability to repel liquids, possessing a broad range of surface tensions, offers the potential to be used for the protection of various surfaces, including glass, keeping them dust- and dirt-free through the physical self-cleaning mechanism. We report the production of a coating which combines liquid amphi-repellency (i.e. physical self-cleaning) with phtotocatalytic activity (i.e. chemical self-cleaning, induced by the UV-A radiation). Consequently, the produced coating has an enhanced self-cleaning capacity which originates from two different (physical and chemical) mechanisms. As the coating is designed for glass protection attention is focused on maintaining optical transparency of glass. The coating consists of a fluorosilane (1H,1H,2H,2H-perfluorooctyltriethoxysilane) and titanium oxide (TiO2) nanoparticles. The effects of (i) the number of dip coating cycles which were applied to treat glass and (ii) the concentration of TiO2 nanoparticles on optical transparency, wetting properties (i.e. physical liquid repellency) and photocatalytic activity are investigated. A coating which was prepared with two coating cycles and 0.25% w/w TiO2 NPs was selected, as it combines optical transparency, amphi-repellency and photocatalytic cleaning. The selected coating shows very good mechanical stability against abrasion, resistance to degradation effects induced by the UV radiation, chemical stability, stain resistance and anti-smudge performance.