Paint that never fades? Bird feathers hold the answer

Pick up any old photograph at home. It could be that photo your father always pulls out of his wallet whenever he tries to convince you that you look so much like your mother, or a snapshot taken at the beach or the zoo, back when you were still a toddler. Take a good look at the photo. Chances are, the colors are already faded—or at least beginning to.

Fading happens because paints absorb light energy.

“Most color you get in paints, coatings or cosmetics, even, comes from the selective absorption and reflection of light,” explained Vinothan N. Manoharan, a Gordon McKay Professor of Chemical Engineering and Professor of Physics at Harvard's School of Engineering and Applied Science. “What that means is that the material is absorbing some energy, and that means that over time, the material will fade.”

Interestingly, though, bird feathers don’t seem to have that problem: they can maintain their bright hues for centuries with virtually no difference in color quality. Unlike photographs, posters, or paintings, bird feathers don’t rely on energy-absorbing pigments that degrade over time; rather, they contain nanostructures with tiny pores arranged in such a way as to amplify specific wavelengths of light. The resulting hues are known as structural color.

This is why Manoharan and his team decided to focus on recreating this effect using microparticles suspended in a solution, in an attempt to eventually develop paint (or even full-color displays) in colors that will never lose their vibrance.

"We think it could be possible to create a full-color display that won't fade over time," says Manoharan. "The dream is that you could have a piece of flexible plastic that you can put graphics on in full color and read in bright sunlight." This experiment was inspired by the cotinga, a bird whose feather pores lack the opal-like, crystalline arrangement often found in systems that generate structural color.
 

By carefully constructing a system of microcapsules filled with a solution of disordered particles suspended in fluid, Manoharan’s team was able to observe how the particles reflected color depending on the condition of the microcapsules. As the microcapsule is gradually dried out, it decreases in size and subsequently shrinks the distance between the particles. The new average distance results in the appearance of a single, specific reflected color from the capsule. Further shrinking results in a different color.

“There’s an average distance between particles, even though there is no ordering in the particles,” says Manoharan. “It’s that average distance that is important in determining the color.”

While the process is still in its experimental stages, further success in this pursuit could mean a lot for tomorrow’s gadgets, specifically in terms of how they register and display colors on their screens. The team's findings were published online in the journal Angewandte Chemie. — TJD, GMA News