A non-fluorinated superhydrophobic PDMS/STA/TiO2 coating with photocatalysis and environmental stability properties by one-step cold spraying

Constructing a titanium dioxide (TiO2) superhydrophobic surface that is both environmentally friendly and long-term stable, while also possessing photocatalytic properties, is a considerable challenge. In this work, instead of a perfluorinated modifier, we used stearic acid (STA) to modify TiO2 nanoparticles. The particles were further utilized to facilitate the rough structure of superhydrophobic surfaces, making these surfaces fluoride-free and environmentally friendly in practical applications. STA/TiO2 nanoparticles and Polydimethylsiloxane (PDMS) were mixed in an ethyl acetate solution to form the PDMS/STA/TiO2 emulsion, which was used to prepare the PDMS/STA/TiO2 coating by a one-step cold spraying. PDMS was introduced into the coating, providing the lower surface energy, adhesiveness, and protection from photo-oxidative damage. It is found that the non-fluorinated PDMS/STA/TiO2 coating exhibits good superhydrophobicity with a water contact angle of 159.7 degrees and a sliding angle of 2.9 degrees. Under ultraviolet (UV) irradiation, the coating displayed excellent photocatalytic degradation activity towards Methylene Blue, Methyl Orange, and Nile Red dyes. Moreover, the coating can withstand sandpaper abrasion, high temperatures and exposure to droplets of different pH values, indicating good chemical, mechanical and thermal stability. The coating presented strong durability, maintaining its super-hydrophobicity even after being exposed to air for 3 months or UV irradiation for 5 h. Besides, the coating demonstrates good self-cleaning performance and adaptability. The large-area superhydrophobic surface made by simple and convenient one-step cold spraying is expected to have practical applications in shipbuilding, construction, textiles, and other industries.