A ghostly beetle could help engineers create brilliantly white materials.
A beetle's whiter shade of pale. I'm Bob Hirshon and this is Science Update.
One of nature's whitest creatures is a small Southeast Asian beetle. Optical physicist Pete Vukusic of the University of Exeter in England is learning how the beetle's thatched scales create such a pure white effect. He notes that each scale is only one two-hundredth of a millimeter thick, or about 50 to 100 times thinner than paper.
Generally speaking, such brilliant whiteness can only be produced from a thick layer, such as a few feet of snow or a few millimeters of enamel on teeth.
In a new report, he describes how the filaments within the scales scatter light so well. If that can be re-created commercially, it could be used in a number of applications, from paint and dental implants to new flat light panels, that will need very thin reflective backings to scatter their light across a room. I'm Bob Hirshon, for AAAS, the science society.
Making Sense of the Research
This research gets into the everyday physics of color. All the colors we see around us are created by the chemical and physical structure of the material we're looking at. The specific arrangement of the molecules in that material will either absorb or scatter every possible wavelength of visible light. The light that's scattered back to our eyes—green, for example, in the case of grass—creates the color. If no visible light scatters, the object looks black. On the other hand, if most or all wavelengths of visible light scatter, the object looks white.
It turns out that there aren't many natural materials that scatter all wavelengths of light equally well. When we do see white in nature, as in snow, a dove's feathers, or a polar bear's fur, it's often created by multiple layers of material that isn't quite so white on its own. (Spread a thin layer of snow out on your hand, for example, and it will look more transparent than white.) The same is true of this beetle, which owes its white color to thin, overlapping scales that cover its body like roof tiles.
What's remarkable about the beetle, though, is how incredibly thin those scales are, especially since they create one of the whitest materials in nature. It's whiter than a baby tooth, and only about 25 percent less white than printer paper, which is 50 to 100 times thicker.
Vukusic's team figured out what makes the scales so white by comparing them to the scales of a related beetle which comes in rich colors. They found that while the colorful beetles' scales were made up of relatively organized three-dimensional fibers, the white beetles' scales were made up of randomly scattered filaments, which help to randomly scatter different wavelengths of light. They also found that these fibers tended to be spaced a little farther apart than the mineral particles that are added to paper to make it whiter, suggesting that paper could be made whiter still by tinkering with its chemistry.
It's easy to think of cosmetic uses for inexpensive, super-thin white materials: white paints that need only a single, thin layer to coat a room; white surfaces for false teeth; white plastics for mp3 players and cell phones. But Vukusic mentions another, potentially more significant application: energy-saving flat light panels. He notes that the technology exists now to create these ultra-efficient, flat light sources called "light-emitting diodes." These panels would look like a glowing mirror that you might hang on a wall. However, if you simply hung the light panel itself, half the light would be lost because it would shine into the wall rather than the room. So in order to perform at their best, these panels require white backings to scatter that backwards-projected light into the room. If scientists can steal the beetle's secrets to create ultra-thin backings for these panels, they'll be able to use them in a much wider variety of settings.
Now try and answer these questions:
- What makes a material white?
- Why do this beetle's scales stand out among other naturally white materials?
- How does the molecular structure of the scales contribute to the beetle's white color?
- What are some applications for ultra-thin, brilliant white materials? Can you think of others that weren't mentioned?
You may want to check out the March 2, 2007, Science Update Podcast to hear further information about this Science Update and the other programs for that week. This podcast's topics include: using ultrasound to find expensive wood, how cheese is helping to fight a tree fungus, the connection between prostate cancer and a lack of male sons, the division in your brain, and the secret to an ultra-white beetle.
The Physics Classroom lesson plan, Light Waves and Color, features information about light. The information is organized into two lessons and covers topics including wave-like behaviors of light, visible light, color, and more.
The Franklin Institute's online exhibit, Light and Color, covers topics such as rainbows, the visible spectrum, the electromagnetic spectrum, and color blindness.
The National Geographic News articles Will "Gecko Tape" Let Humans Climb Walls? and How Geckos Stick describe another natural wonder that may inspire new materials, while the article Peacock Plumage Secrets Uncovered describes efforts by physicists to understand the brilliant colors of peacock feathers.