Enhanced wettability and wear resistance on TiO2/PDA thin films prepared by sol-gel dip coating

Abstract

An enhancement in the wettability and wear resistance of titanium dioxide (TiO2) thin films was obtained by combining a polydopamine (PDA) adhesive layer between TiO2 layer and glass substrate. The coating layers of TiO2 thin film, prepared from sol-gel precursor, were deposited on PDA precoated glass substrate by sol-gel dip coating technique. The wettability of films was evaluated by testing the water contact angle and adhesion force between an atomic force microscope (AFM) tip and film surface. The results indicate that the hybrid TiO2/PDA thin films, compared to pure TiO2 thin films, exhibit higher wettability. UV–visible absorption spectra showed the wider absorption range in TiO2/PDA thin films, which means more oxygen vacancies may be induced by light irradiation and are favorable for the absorption of water molecules, thus enhancing the hydrophilicity of the films. The wear resistance and indentation tests were performed by scratching the film surface with the AFM probe and a NHT nanoindentor, respectively, indicating that the hybrid TiO2/PDA thin films have more wear resistance than the pure TiO2 thin films, due to the formation of a mixed layer consisting of TiO2 and PDA that increases the adhesive force of TiO2 layer to the substrate.