Scientists have created a flat surface patterned after the body hair of spiders that refuses to get wet.
The surface also has the added benefit of being self-cleaning, since water does a pretty good job of picking up and carrying off dirt as it is being repelled.
This makes the material ideal for some food packaging, windows, or solar cells that must stay clean to gather sunlight, scientists say. Boat designers might someday coat hulls with it, making boats faster and more efficient.
But what makes the new surface really unique is that unlike other similar products out there, such as shoe wax and car windshield treatments, the new material doesn’t rely on chemicals with water-repellent properties to stay dry. Instead, its surface blocks out water by mimicking the shape and patterns of a spider’s body hair. In other words, physics, not chemistry, is what keeps it dry.
Spiders "have short hairs and longer hairs, and they vary a lot. And that is what we mimic,” said Wolfgang Sigmund, a professor of materials science and engineering at the University of Florida.
It’s been long known that spiders use their water-repelling hairs to stay dry or avoid drowning. Water spiders use their hairs to capture air bubbles and tote them underwater to breathe. But it was only five years ago that Sigmund began experimenting with microscopic fibers, turning to spiders for inspiration.
At first, Sigmund's natural tendency was to make all his fibers the same size and distance apart. But he later learned that the pattern of hairs on a spider’s body consists of both long and short hairs that are both curved and straight. So he decided to mimic Nature and replicate this random pattern using plastic hairs varying in size but averaging about 600 microns, or millionths of a meter.
“Most people that publish in this field always go for these perfect structures, and we are the first to show that the bad ones are the better ones,” Sigmund said.
The technique, detailed in the science journal Langmuir, can be applied to keep even absorbent materials like sponges from getting wet. It may also be safer than other forms of water-proofing since the method doesn't involve the use of chemicals.
Sigmund says that he has even developed a variation of the surface that repels oil. However, he noted that the process is not reliable enough to continually create good working surfaces, and different techniques need to be developed to produce such surfaces in commercially available quantities and size.
“We are at the very beginning,” Sigmund said. “But there is a lot of interest from industry, because our surface is the first one that relies only on surface features and can repel hot water, cold water, and if we change the chemistry – both oil and water.”
