Photoactive sol-gel hybrid coatings from modified fluorocarbon polymers and amorphous titania

A series of organic???inorganic hybrid coatings was prepared through sol???gel chemistry by combining silanized chlorotrifluoroethylene-vinylether (FEVE) binders with tetraalkoxy silicon and titania sols under acidic conditions. The best compositions to obtain highly transparent and homogeneous coatings after thermal curing were determined. All the hybrid coatings easily pass the MEK test and show high scratch hardness. The atomic force microscopy (AFM) shows the formation of very smooth surfaces (Rrms routinely <1 nm) without clear phase separation phenomena. The typical size of the ???objects??? which may be individuated is in the range of 40???80 nm. Wettability through contact angle measurements shows the formation of moderately hydrophobic surfaces with a low contact angle hysteresis (???20???) which is a further indication of very smooth, homogeneous and chemically stable surfaces. After irradiation with UV-B light only hybrid coatings containing titania phases show a significant switch to a superhydrophilic behavior with a contact angle against H2O down to 6???, which is only partially recovered after storage of the material in the dark. Titania based hybrid coatings also showed a fast and efficient UV-induced discoloration of the resazurin ink. The formulation of the coatings with photostabilizers belonging to the class of radical scavengers and UV absorbers does not change the photoinduced surface properties while eliminating the yellowing of the coating after UV exposure. It is concluded that titaniafluoropolymer hybrid coating show photoactivity and UV-induced superhydrophylicity mostly through ionic mechanisms, which could be beneficial to develop high durability and self-cleaning protective coatings.