[Image above] A self-cleaning paint developed by researchers at University College London allows droplets to pick up dirt as they roll across treated surfaces. Credit: Yao Lu; UCL

Scientists at University College London (UCL) have developed a paint made from coated titanium dioxide nanoparticles that creates self-cleaning surfaces that can be abused by and withstand even the most abrasive and damaging treatment.

According to a UCL news release, the team, which also included researchers from Imperial College London and Dalian University of Technology (China), developed a paint that “creates a more resilient surface that is resistant to everyday wear and tear [and] so could be used for a wide range of real-world applications, from clothing to cars.” The findings are published in Science.

Standard self-cleaning surfaces (see here, here, and here) repel water but recoil in the face of damage or exposure to oil.

Not this paint.

Not only can the superhydrophobic coating be applied to clothes, paper, glass, and steel, but it can stand up to conditions that would normally force other self-cleaning coatings into submission—wiping, scratching, and a whopping 40 abrasion cycles with sandpaper.


Dyed-water droplets sit on the surface of treated cotton wool. Credit: Oli Usher, UCL

“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,” says first author Yao Lu of UCL in the release. “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 to help the surfaces withstand damage.”

The team used different methods to coat different surface materials, including an artist’s spray-gun to apply the coating to glass and steel, dip-coating to apply onto cotton wool, and a syringe to coat paper. 

No matter the method, however, the titanium dioxide coating made each surface waterproof, allowing water droplets to bead up and wipe away dirt particles as the droplets rolled away. And even after taking the researchers’ abuse, the surface coatings still worked. 

“Our paint worked extremely well for a variety of surfaces in tough conditions, which were designed to simulate the wear and tear of materials in the real-world,” adds Lu. “For example, car paint frequently gets scuffed and scratched and we wanted to make sure our paint would survive that. As well as practical uses, the paint could also be used creatively to make art with water, which is something I have been exploring in my own time.”  

Credit: UCL Mathematical and Physical Sciences; YouTube

What does their work mean for the continued development of self-cleaning surfaces?

“The biggest challenge for the widespread application of self-cleaning surfaces is finding a way to make them tough enough to withstand everyday damage,” says UCL professor and coauthor Claire Carmalt. “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. We used materials that are readily available so our methods can be scaled-up for industrial applications.”

The researchers say they are hopeful that the work will help advance widespread adoption of self-cleaning surfaces. In the meantime, they continue to work on advancing a “broader portfolio of surfaces.”

The paper is “Robust self-cleaning surfaces that function when exposed to either air or oil” (DOI: 10.1126/science.aaa0946).