Common to Central and South America, the Blue Morpho is an iconic butterfly, prized for its brilliant blue color and iridescence. Beyond its beauty, however, scientists have discovered that its wings have a certain microscopic texture that could benefit a wide range of applications from self-cleaning instruments, to more efficient piping.
For example, the researchers were able to clean up to 85 percent of dust off a coated plastic surface that mimicked the texture of a butterfly wing, compared to only 70 percent off a flat surface. The Blue Morpho is a highly fragile, light weight insect, so even a few specs of dust or drops of moisture can overburden it and cause a huge energy consumption. Upon inspection by electron microscope, the scientists found that the butterfly’s wings are far from being smooth like they might seem with 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,” the authors say. Check out these electron microscope images zoom by zoom.
“Nature has evolved many surfaces that are self-cleaning or reduce drag,” said Bharat Bhushan, Ohio Eminent Scholar and Howard D. Winbigler Professor ofmechanical 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.”
In addition to the Blue Morpho, the Ohio State researchers also analyzed leaves of the rice plant Oriza sativa, which also exhibits an interesting self-cleaning texture – rows of micrometer- (millionths of a meter) sized grooves, each covered with even smaller, nanometer- (billionths of a meter) sized bumps; this construction directs raindrops to the stem and down to the base of the plant. Plastic replicas of both microscopic textures were cast and compared in their ability to repel dirt and water to replicas of fish scales, shark skin, and plain flat surfaces.
To test the capabilities of these textures, with respect to other known industry useful texture or simple control texture (smooth), the researchers devised plastic pipes the sized of a cocktail straw with the different coated textures and pushed water through them. The resulting water pressure drop in the pipe was an indication of fluid flow.
A thin lining of shark skin texture coated with nanoparticles reduced water pressure drop by 29 percent compared to the non-coated surface. The coated rice leaf came in second, with 26 percent, and the butterfly wing came in third with around 15 percent.
That was the easy part. Next, the scientists simulated applications where environmental contaminants like dirt are present. So, the dusted each of the textures with silicon carbide powder, an industrial powder that resembles dirt, and tested them out. 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 and then, 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 percent of the particles washing off during the test. Next came the rice leaf, with 95 percent, and the butterfly wing with about 85 percent washing off. By comparison, only 70 percent washed off of the flat surface.
The authors believe the rice leaf texture might be especially suited to helping fluid move more efficiently through pipes, such as channels in micro-devices or oil pipelines, while the Blue Morpho’s clapboard roof texture might suit medical equipment, where it could prevent the growth of bacteria.
Findings were published in the journal Soft Matter.