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Need Extraordinary Materials? Look to Nature

A gecko's toes stick to a pane of polished glass like glue, allowing it to scurry straight up a window. An ant floats on water and a water-strider walks on it. Raindrops falling on the leaves of a lotus plant form into tiny spheres and roll away carrying dirt with them. The iridescent blue and green wings of tropical butterflies attract mates and intimidate enemies.

Like wizards in a Harry Potter novel, scientists use these butterfly wings, ant's hairs and gecko's feet to conjure up their own 'magic' materials. Of course no actual reptiles are used to manufacture these new goods; they are simply studied under a microscope! The natural properties that are seen provide the inspiration for researchers working in the field known as materials science to build their own surfaces with the same extraordinary properties.

Gecko toes, when magnified tremendously, consist of millions of hairs each 100 times thinner than a human hair (pictured below). Like shag carpet, the hairs have a huge surface area of tiny pointed tips that can catch on the smallest flaws in the glass surface. This causes an enormous amount of friction and keeps the foot from slipping.
 
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Another microscopic rough texture keeps the leaves of the lotus clean. In this beautiful image, you can see it: a pattern of cone-shaped structures bristling with tiny bumps too small for dirt to fall between. Water too is not at home on this prickly surface, and droplets squeeze tightly together into a bead to touch it as little as possible. This bead does not stick and can easily move about on the surface. As the bead rolls across the leaf, the pieces of dirt that it rolls over stick to it and are carried away. Surfaces with this property are called hydrophobic (water-fearing).

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Ants and water-striders too use extremely rough surfaces to avoid water. The butterflies use a different pattern: rows of tiny trenches that only reflect certain colors and not others. These trenches provide a blueprint for optics known as 'diffraction gratings' that can split light into different colors and reflect only certain shades.

After observing these structures carefully, scientists have gone to work copying them with the latest technologies for imprinting surfaces with extremely tiny patterns. Just recently, one of the first commercial 'superhydrophobic' products began testing: anti-stain spray! This spray allows the wearer to pour chocolate sauce, grease or tomato juice onto cloth and watch it bead and shoot off just like rain on a lotus plant, without leaving a mark.

Images: (1) Central Michigan University Microscopy Lab; (2) Hong-Kong University Physics: hky-phy.org


Tom Hartsfield
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