New self-cleaning paint offers stain and damage-free future

[May 05, 2015]  By Matthew Stock
 
 A self-cleaning paint that can withstand contact with substances such as oil, even after being scratched or scuffed with sandpaper, has been developed by British and Chinese researchers.

The coating was devised by University College London (UCL) researcher Yao Lu and his supervisor, Professor of Inorganic Chemistry Claire Carmalt, and can be applied to clothes, paper, glass and steel. When combined with adhesives, its self-cleaning properties remain, in spite of attempts to scratch or scuff it.

Self-cleaning surfaces work by being extremely repellent to water but are often rendered useless once damaged or exposed to strong substances like oil. Yet the self-cleaning properties of this new coating, made from titanium dioxide nanoparticles, work during and after immersion in problematic substances and following surface damage.

Yao developed an interest in developing the paint having become fascinated with the superhydrophobic - or water repelling - properties of plants, such as lotus and taro leaves. "I am quite interested in self-cleaning coatings in nature, such as plants," said Yao. "We put water on superhydrophobic plants, water wouldn't wet them. Instead the water will form drops and then roll off or just bounce away and leave the surface dry and clean."

The researchers say the new paint creates a resilient surface resistant to wear and tear, that could be used for real-world applications such as clothing and cars. They say that having completely water-resistant surfaces allows water to form marble-shaped droplets that roll over the surface, acting like miniature vacuum cleaners picking up dirt, viruses and bacteria.

According to Carmalt, "water is dropped onto the surface. It actually forms near spherical shaped balls which, as they roll across the surface, act like miniature vacuum cleaners picking up dirt and bacteria, and we can take that paint and we can adhere it onto hard surfaces like glass or metal, or soft surfaces like cotton and paper just using simple adhesives."

She added that the roughness of the surface is created by having two different sizes of titanium dioxide nanoparticles, with the waxy texture formed by adding fluorosilane.

The experiments were filmed to show the behavior of the treated surfaces. One video shows treated paper remaining dry and clean after being exposed to dirt and water.

Carmalt says the biggest challenge for the widespread application of self-cleaning surfaces is finding a way to make them tough enough to withstand everyday damage. She said the UCL team's coating is superior to other superhydrophobic substances available. "I think the improvement is the fact that we get this very resistant coating, so generally these superhydrophobic coatings are very mechanically weak, so can be easily rubbed off over time, whereas by applying this spray adhesive we've managed to get very resistant coatings that are resistant to, as I say, rubbing or scratching and with sandpaper and so on," she said.

Carmalt says the process could easily be scaled-up for industrial applications, such as car spray paint. It could also be used in antimicrobial coatings to combat hospital acquired infections.

The study, which also involved researchers from Imperial College London and Dalian University of Technology (China), was published recently in Science.

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