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'Butterfly wing' buildings would never need painting

A drop of water sits on a piece of a new, colorful, water-resistant material.
A drop of water sits on a piece of a new, colorful, water-resistant material. The material's texture mimics that of butterfly wings, causing water to bead.AFM

A new material inspired by butterfly wings repels water and gleams with brilliant color. Like iridescent butterflies, the material uses tiny structures on its surface to achieve both qualities. 

A material that's both colorful and water-repelling could someday go into sensors that regulate the interior temperature of "smart buildings," said Shu Yang, a University of Pennsylvania chemist whose research group made the new material. 

Color may come quickly to mind when people think about butterflies, but the little flutterers are remarkably water-resistant, too. "They have to fly, so they cannot afford to have any dirt on the wings," Yang told TechNewsDaily. The surface of butterfly wings has minuscule bumps that cause any water that hits the wing to form beads and roll away, Yang explained. That cleans off the dirt.

Yang and a team of architects and engineers are looking to make a sturdy sensor that changes color in response to temperature. The color change would trigger a computer program that automatically adjusts the heaters and air conditioners of a smart building. "The general goal is for energy-efficient buildings," Yang said. 

Her material also could go on the outside of buildings, to provide colorful designs that are more durable than conventional paint and that resist dirt and mildew, she said. 

The color in the new material — as in its insect inspiration — doesn't come from the pigments and dyes that color most household items. Instead, the material's particularly bright hues come from well-ordered ridges and other structures that are invisible to the naked eye. The complex structures reflect light in particular ways, creating different colors that people see. 

Scientists call such colors structural color. They can last longer than pigments because they don't fade in the sun. "As long as you don't destroy the structure, the color is always there," Yang said.

At the same time, to make a material waterproof, Yang's team needed to make the surface rough and bumpy. The roughness isn't apparent to the touch because the bumps are nano-sized, but the tiny textures reduce water's ability to stick to the material. 

Yang and her research team created a recipe for making a material that has both the patterned ridges for structural color and the nano-bumps for waterproofing. The researchers are now looking to change their manufacturing process to make it less expensive.

Yang's research projects usually focus on just structural color or just waterproofing, not both, she said. But "in nature, in all of these things, it's not just single-functional," she said. "It always is multifunctional."

 Yang and her colleagues published a paper about their work in the July issue of the journal Advanced Functional Materials.

You can follow TechNewsDaily staff writer Francie Diep on Twitter @franciediep. Follow TechNewsDaily on Twitter @TechNewsDaily, or on Facebook.

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