Expanding the use of functional coatings

Today’s coatings are no longer just for decoration or protection, researchers are pushing the limits by incorporating additional properties such as low microorganism-adherence, ease of cleaning or self-repair properties.

The phase separation in the copolymer: when the siloxane (areas where yellow predominates) migrates to the surface, it generates greater roughness, and due to its hydrophobic characteristics, prevents the adhesion of organisms. Photo Courtesy of Alexander Santiago/UPV/EHU.

These “functional coatings” calls for the control of their physical properties as well as the chemical ones of the surfaces produced.

The research of Alexander Santiago set out to develop three types of functional coatings: ones that are resistant to microorganisms (for example for paints for seagoing vessels), and which have self-cleaning (hydrophobic paints) and anti-reflecting properties (for coating mobile phone screens or spectacle lenses).

The first of the hydrophobic coatings he explored was a type of copolymer that gives rise to spontaneous phase separation between its components.

“One of the components of the copolymer (the polyurethane) gives the substrate adhesion and most of the other component (the siloxane) remains on the surface, which makes it rougher, and as it is also hydrophobic it stops organisms sticking to it,” explains Alexander Santiago.

The research determined that the hydrophobicity of the system depended to a greater extent on roughness than on the siloxane concentration on the surface and that the microorganisms stuck less to the films displaying phase separation.

The second type of functional coatings Santiago explored was those that would display a self-cleaning effect. Inorganic nanoparticles of a hydrophobic nature were synthesized in advance and inserted into acrylic polymers using various methods. Specifically, they were silicon nanoparticles with an organic coating.

Santiago obtained the best results by spraying these nanoparticles onto acrylic films, and that way a super-hydrophobic surface was created offering very good self-cleaning properties in addition to a high level of toughness. This method was fast and relatively cost effective as silicon is less expensive than other substances on the market.

To obtain anti-reflecting properties, the films need to have a refractive index lower than that of the substrate, which can be achieved by inserting porosity into them. The porosity/toughness relation was studied with respect to the refractive index obtained and the results were promising.

The researcher notes that there is still work to be done. “For example, the nanoparticles do not take hold completely and because the final film with the nanoparticles is not as consistent as we would like.”

Early results were favorable for the copolymers studied in relation to the biological anti-contamination properties. Finally, the researcher explained that the subject of anti-reflective coatings was only at the early stages of research and “we are still improving it.”

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