British and Chinese scientists say they have developed a new paint that can be applied to clothes, paper, glass and steel to make resilient surfaces that can self-clean even after being scratched or scuffed. In research published in the journal Science on Thursday, the scientists said the paint, made from coated titanium dioxide nanoparticles, is extremely repellent to water but, unlike other waterproof coatings, continues to work even when damaged or exposed to oil. Because it is so hard-wearing, it could be used for a wide range of applications, from clothing to cars. "The biggest challenge for self-cleaning surfaces is finding a way to make them tough enough to withstand everyday damage," said Claire Carmalt, a professor of inorganic chemistry at University College London, who co-led the research. "The surfaces tend to be mechanically weak and so rub off easily. But by pairing our paint with different adhesives, we've shown it is possible to make a robust self-cleaning surface." In their experiments, Carmalt's team used different coating methods to create repellent surfaces, depending on the material. To coat glass and steel, they used a spray-gun, for cotton wool they used dip-coating, and for paper a syringe. "Being waterproof allows materials to self-clean, as water forms marble-shaped droplets that roll over the surface, acting like miniature vacuum cleaners picking up dirt, viruses and bacteria along the way," said Yao Lu of UCL's chemistry department, who co-led the study. "For this to happen the surface must be rough and waxy, so we set out to create these conditions on hard and soft surfaces by designing our own paint and combining it with different adhesives." The team's results showed that in all cases, the materials became waterproof and self-cleaning, with water droplets of different sizes bouncing off them and taking dirt with them. This continued even after the materials were scratched with a knife or scuffed with sandpaper.
