Self-Cleaning Surfaces: How Nature is Inspiring Scientists
Key Highlights :
Nature is an ever-inspiring source of ideas for scientists. Recent research has looked to the humble cicada for a solution to the never-ending battle against dirt and dust. By studying the insect's self-cleaning wings, my team has discovered a mechanism that could help us keep our car windows spotless without any effort.
The cicada's wings are covered in a complex arrangement of thousands of tiny wax-coated cones. These cones cause water droplets to assume a bead-like shape, which helps them to remove dust particles and microorganisms as they collide with each other or roll down the insect's wings.
Butterflies, geckos, and certain plant leaves, such as lotus and rice, also use droplet motion to keep themselves free from dust. These moving droplets also help remove bacteria, thus lowering the risk of infections.
The process of self-cleaning is made possible thanks to something engineers call "super-hydrophobicity" or extreme water-repellency. The wax on the cicada wings repels water and the conical tips prevent spherical water droplets from penetrating into the wing membrane. This is similar to a fully blown balloon placed over a bed of nails, where the pressure is distributed over all the nails.
In the case of droplets, the wax-coated cones facilitate effortless droplet movement on cicada wings. Larger droplets roll down cicadas' waxy wings, picking up numerous contaminants along their journey. However, until now, how smaller droplets, which are too small to be pulled by gravity, picked up dirt remained elusive.
Our study revealed that small droplets, over time, will merge with their neighbors. The merged droplet jumps off the surface instead of rolling off. During the jump, the droplet will assume a shape that resembles a hot-air balloon about to take off from the ground. This hot-air balloon shape is crucial for enabling droplets to carry dirt away from the surface. It turns out that it is the surface tension of the liquid droplet that picks up the dirt while the droplet is in the hot-air balloon shape.
In the future, engineers can incorporate what we have learned about cicada wings into product designs. This could mean that things like skyscraper windows, solar panels, and surveillance camera lenses could clean themselves. Super-hydrophobic coatings could also help prevent frost formation on various surfaces in winter, such as car windscreens.
Nature is all around us, even in the most urban areas. By studying the natural world, scientists can continue to develop innovative solutions to make our lives easier.
