Water-repellent material sheds like a snake when damaged
What if materials could heal scratches by shedding part of the damaged outer layer? Researchers at the University of Freiburg in Germany have developed a water-repellent material that moults like a snake skin when damaged, revealing another hydrophobic layer beneath it.
Water-repellent materials are often made by coating a substrate with nanostructures, sometimes shored up by adding microstructures. These hydrophobic surfaces have many useful applications, such as rain gear, medical instruments, or self-cleaning car windows. However, most of these materials scratch relatively easily.
The researchers found a solution in nature, by looking at snake and lizard skins. About once a month, a snake will shed its entire skin, leaving behind the old skin, along with any damages and parasites.
The new material works similarly. It consists of three layers. The top layer is of a hydrophobic film made of poly-1H,1H,2H,2H-perfluorodecyl acrylate (PFA), also known as “nanograss,” which gains its water repellent properties from sharp, cone-like nanostructures that stick up from its surface. Under this is a layer of polyvinylpyrrolidone (PVP), a water-soluble polymer used in various medical applications. At the bottom is a superhydrophobic silicon nanograss film.
The idea is that if the top layer is scratched, the material can be submerged in water. The water seeps into the scratch and dissolves the intermediate polymer layer. By doing so, the top layer becomes loose, exposing a fresh hydrophobic layer beneath. Of course, unlike snakes, this process can only happen once, unless multiple hydrophobic layers are applied.
According to the team, the skin-shedding material is still very much in the laboratory stage and more work needs to be done to strengthen the top layer to prevent a scratch damaging the lower layers. But if they’re successful, their shedding material could lead to more resilient self-cleaning and water-repellent materials.
Images: ACS (via New Atlas)