Thursday, 18 October 2012 07:25
October 18, 2012
From children running around the park to scientists bent over their collections, people have long been fascinated by the brilliant and colorful patterns on butterflies' wings. While bright colors and strange patterns are hardly unique in nature, butterflies actually do stand apart in how they make these beautiful displays.
And for the first time, researchers at the University of Pennsylvania have found a way to mimic these designs.
Unlike the bird feathers, mammal fur or the paints humans use, butterfly wings get their color from the nano-scale structure of the surface. Intricate periodic lattices are created that bend, block or otherwise modify light to create specific wavelengths of light, leading to particularly vivid colors.
Because they are extremely rough and allow for minimal contact with flat surfaces, these complex structures have an added benefit of making butterfly wings superhydrophobic, meaning that they are extremely resistant to water.
"A lot of research over the last 10 years has gone into trying to create structural colors like those found in nature, in things like butterfly wings and opals," Shu Yang, the head of the group at UPenn, said in a statement. "People have also been interested in creating superhydrophobic surfaces which is found in things like lotus leaves, and in butterfly wings, too, since they couldn't stay in air with raindrops clinging to them."
Both attributes - vivid colors and water resistance - could be extremely commercially useful, with everything from electronic devices to buildings looking to incorporate better ways to discourage water. Superhydrophobicity has the added benefit of making it extremely easy to clean surfaces.
To create the effect, UPenn's engineering research led the team to use a process known as holographic lithography. This process uses lasers to create a three-dimensional pattern similar to those found in a butterfly's wing within a material known as a photoresist.
These patterns are then carved out by a solvent, which clears away any of the base material that was not exposed. Then a lower-quality solvent is used that causes the structure to shift in a way that creates the extremely rough texture.
"The good solvent causes the structure to swell," Yang explained. "Once it has swollen, we put in the poor solvent. Because the polymer hates the poor solvent, it crunches in and shrivels, forming nanospheres within the 3D lattice."
The new approach could be applied to surfaces ranging from solar panels to simple wall facades.
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