Synthesis and surface functionalization of titania nanocrystals for low temperature deposition on polymers

A thin film of crystalline titanium dioxide applied as a self-cleaning coating is a versatile system due to its properties of being transparent and colourless, chemically stable, non-toxic and relatively cheap. Most importantly it has the ability to become photocatalytically active and superhydrophilic upon UV-irradiation. These self-cleaning coatings can mitigate staining, fogging and the odour and deterioration caused by dirt. This results in the fact that self-cleaning coatings are an important topic in research, and are highly commercially relevant. In this work, we extend the use of these coatings to polymers, since this opens up a large market of self-cleaning coatings for applications such as (touch)-screens, visors, light-domes and noise barriers on highways. This transition to polymer substrates, however, poses some challenges. It is imperative for the photocatalytic properties that the TiO2 thin film is of the anatase crystal phase. In order to induce crystallinity to a film deposited from a precursor solution, these films need to be subjected to elevated temperatures (>400°C). This is incompatible with the use of polymers as substrates, since these high temperatures will cause deformation or deterioration of the polymer substrate. In order to circumvent this issue, films are deposited on the substrates from colloidal suspensions that already contain anatase nanocrystals. Other challenges are the wettability of the polymer surface by the colloidal suspension and the durability of the coating. Therefore, the use of chemical linkers to bind titania nanocrystals to the surface of a polymer substrate is explored. This covalent linking is envisioned to improve the durability of the final titania coating.

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