Nanotech Innovation Keeps Surfaces Clean and Transparent

Hanging hundreds of feet off the ground to wash a skyscraper’s windows or pumping water out to a desert solar array to keep its panels and mirrors clean is more than just a hassle—it’s an expensive problem with serious ecological implications.

A spin-off company from Penn has found a way to solve the problem of keeping surfaces clean, while also keeping them transparent.

Nelum Sciences, created under an UPstart program in Penn’s Center for Technology Transfer, has developed a superhydrophobic coating that can be sprayed onto any surface. The water-based solution contains nanoscopic particles that add a nearly invisible layer of roughness to a surface. This increases the contact angle of the material to which these particles are applied.

A contact angle is the angle the edges of a resting drop of liquid make with a surface. When the angle is low, a drop resembles a flattened hemisphere, with edges that are stuck to the surface. But as the angle increases, a drop begins to look more like a ball, until it literally rolls away instead of sticking.

When these balls of liquid roll off a superhydrophobic surface, they pick up any debris they encounter in their paths, keeping a surface clean.

Co-founded in 2011 by Shu Yang, professor of materials science and engineering in Penn’s School of Engineering and Applied Science, Nelum Science’s coating is based on her nanotechnology research. Fabricating the coating’s nanoparticles at sizes smaller than the wavelength of light—the quality that makes them transparent—is the product of cutting-edge laboratory techniques. The company’s inspiration, however, came from structures created by nature.

“Some plants, like lotuses, and other biological structures, like butterfly wings, have this kind of nano-roughness to keep them clean and dry,” Yang says. “That’s why we named the company after the lotus’ Latin name, nelumbo.”

Other superhydrophobic sprays have recently come on the market, but they give surfaces a hazy, frosted appearance, making them inappropriate for applications where cleanliness is critical, such as windows, lenses, safety goggles, and solar panels.

Text by Evan Lerner
Video by Kurtis Sensenig