The Cyphochilus beetle, a common sugarcane pest in Southeast Asia, boasts stark white scales that are brighter than almost any other substance in nature. Drawing on what they know about the unique structure of the critter’s scales, scientists from the University of Cambridge and Aalto University in Finland have created a new, super-white coating, as Ryan F. Mandelbaum reports for Gizmodo.
Humans typically make bright colors using pigments which absorb some wavelengths of light and reflect others. We perceive different colors—red, green, blue and so on—based on the wavelengths that are reflected back to the human eye. White, on the other hand, scatters all wavelengths with the same efficiency.
According to a press release from the University of Cambridge, most commercially available white products—like sunscreen and paint, for instance—“incorporate highly refractive particles (usually titanium dioxide or zinc oxide) to reflect light efficiently.” These materials are thought to be safe, though studies have suggested that titanium dioxide might have adverse health effects when prepared as nanoparticles. And neither titanium dioxide nor zinc oxide is fully sustainable, due to the compounds' extraction and synthesis processes.
For a more environmentally friendly white, researchers looked to the Cyphochilus beetle. The brilliant white of its scales does not derive from a pigment, but rather from intricate networks of chitin filaments. A molecule that is also found in the shells of mollusks and the cell walls of fungi, chitin can reflect light with high efficiency. As Ben Coxworth explains in New Atlas, the research team copied the structure of the Cyphochilus beetle’s chitin networks by carefully arranging very thin strands of cellulose known as “cellulose nanofibrils.” Their experiment, which is described in a new study in Advanced Materials, produced a super-white coating that is 20 times brighter than paper.
“If you’re painting a wall white, you have to paint a few times,” study author Olimpia Onelli from the University of Cambridge tells Gizmodo’s Mandlebaum. “With our material we can paint it with a 10-micron thickness.” That, as Mandlebaum notes, is thinner than the width of a fine strand of hair.
The new coating isn’t the world’s whitest substance—whiter pigments have been made using titanium dioxide—but in contrast to other materials, it is biocompatible (meaning that it is not harmful to living tissues) and sustainable. The coating isn’t ready for industry use yet, but researchers hope it can someday be applied to a range of products, from cosmetics, to paint, to food.