A South American butterfly flapped its wings, and caused a flurry of nanotechnology research to happen in Ohio and may lead to new high-tech surfaces for aircraft and watercraft, pipelines, and medical equipments.
For example, researchers were able to clean up to 85% of dust off a coated plastic surface that mimicked the texture of a butterfly wing, compared to only 70% off a flat surface. Ohio State University engineers report that textures enhance fluid flow and prevent surfaces from getting dirty.
“Nature has evolved many surfaces that are self-cleaning or reduce drag,” said Bharat Bhushan, Ohio Eminent Scholar and Howard D. Winbigler Professor of mechanical engineering at Ohio State. “Reduced drag is desirable for industry, whether you’re trying to move a few drops of blood through a nano-channel or millions of gallons of crude oil through a pipeline. And self-cleaning surfaces would be useful for medical equipment—catheters, or anything that might harbor bacteria.”
The electron microscope revealed that the Blue Morpho’s wings aren’t as smooth as they look to the naked eye. Instead, the surface texture resembles a clapboard roof with rows of overlapping shingles radiating out from the butterfly’s body, suggesting that water and dirt roll off the wings “like water off a roof,” Bhushan said.
The researchers wanted to test how butterfly wings and rice leaves might display some of the characteristics of other surfaces they’ve studied, such as shark skin, which is covered with slippery, microscopic grooves that cause water to flow smoothly around the shark. They also tested fish scales, and included non-textured flat surfaces for comparison.
In one test, they lined plastic pipes with the different coated textures and pushed water through them. The resulting water pressure drop in the pipe was an indication of fluid flow.
Then they dusted the textures with silicon carbide powder—a common industrial powder that resembles natural dirt—and tested how easy the surfaces were to clean. They held the samples at a 45-degree angle and dripped water over them from a syringe for two minutes, so that about two tablespoons of water washed over them in total. Using software, they counted the number of silicon carbide particles on each texture before and after washing.
The shark skin came out the cleanest, with 98% of the particles washing off during the test. Next came the rice leaf, with 95%, and the butterfly wing with about 85% washing off. By comparison, only 70% washed off of the flat surface.