New self-cleaning paint stands up to wear and tear

Dyed-water droplets sit on the surface of treated cotton wool (Photo: Oli Usher/UCL)

How would you like to be able to wash your car by just hosing it off – no soap, scrubbing or drying? You may be able to in the not-too-distant future, thanks to research being led by a team at University College London. Drawing on earlier research, they've developed an ultra-hydrophobic (water-repelling) paint that can be applied to a variety of surfaces, and that stays on once applied.

The active ingredient in the paint is coated titanium dioxide nanoparticles. These cause liquid to bead up and roll off the paint, instead of clinging to it. As those droplets roll across the painted surface, they suck up any dirt, viruses, bacteria or other non-liquid contaminants that are in their path.

In order to allow the paint to stick to surfaces, it's combined with different types of adhesives, depending on the application. It can also be applied to those surfaces in different ways. In the course of their research, the scientists used an air brush to apply it to glass and metal, a syringe to put it onto paper, and they simply dipped cotton wool into the paint.

Durability has been a limiting factor in many previously-developed self-cleaning paints. In this case, however, the paint remained adhered to the various surfaces and retained its hydrophobic qualities, even after being exposed to conditions designed to simulate real-world wear and tear (this included being scuffed with sandpaper and scratched with a knife). It also kept working after exposure to oil – again, something that can't be said for all of the previous attempts.

Existing technologies such as the Ultra-Ever Dry coating, while relatively robust, do need to be reapplied every few months to a year, depending on the conditions.

"We’ve shown it is possible to make a robust self-cleaning surface," said UCL inorganic chemist Prof. Claire Carmalt. "We used materials that are readily available, so our methods can be scaled-up for industrial applications."

Colleagues from Imperial College London and Dalian University of Technology (China) also took part in the research. A paper on the paint was recently published in the journal Science. You can see the paint shrugging off liquids, in the video below.

Scientists at the University of Rochester, incidentally, have developed a laser-etching technique to render metal surfaces permanently hydrophobic – no chemical coatings required.

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