Anti-fog nanocomposite coatings of enhanced durability

Highly porous nanocomposite films were produced at room temperature from SiO2 or TiO2-SiO2 solutions synthesized by a sol-gel route in the presence of oxide nanoparticles. The photocatalytic behavior of titania-based films was controlled at the sol synthesis step, through three parameters: the relative molar concentration between polymeric and condensed silica, the reactivity of the hydrolysis step, and the relative molar concentration of the active component. The reported method allowed ample tuneability of film refractive index, an important parameter for the design of antireflective and multifunctional coatings. Superhydrophilic properties were demonstrated by the samples and, notably, retained for over 30 days. Experimentally mimicking accelerated surface pollution with olive oil and stearic acid, a strong correlation was found between residual organic contamination, quantified by integrating the film absorption FT-IR spectrum over the C-H-n stretching area, and the measured water contact angle (WCA). Strategies for a fast surface cleaning and restoration of the superhydrophilic behavior via a mild oxidizing agent, based on UV exposure or immersion in a NaClO water solution, were investigated. High wettability can also be obtained through the control of the porosity. This effect has been termed nanowicking: the rapid infiltration of water in an interconnected porous network.