Butterfly wings and opals are some of the most colorful materials in nature. Their color isn’t derived from pigment, but instead from their structures, which reflect light at certain wavelengths that produce specific colors.
Now a group of scientists from the University of Cambridge, in collaboration with Germany’s Fraunhofer Institute for Structural Durability and System Reliability, have mimicked an opal’s nanostructure to produce an elastic polymer that changes color when stretched. The so-called “polymer opals” could be useful in variety of ways, potentially as sensors and dyes.
When naturally formed, opals have silica spheres that settle into hard-packed layers after water evaporates. In the polymer opals, those silica spheres are replaced with nanoparticles that boast a rubbery outer shell. These particles can be linked together to form a thin, elastic sheet with an internal structure that reflects light to produce a single color, depending on how the material is deformed.
Stretching the material causes the space between the nanoparticles to change, thus altering the wavelength at which light is reflected. Therefore, each color can be changed by stretching or twisting the material. Each color produced depends on the size of the nanoparticle used. Check out this hallucinogenic video to see the material change from reddish brown to blue as it’s stretched.
One potential uses for the polymer opal is as a mechanical strain sensor that could measure how much stress an item attached to the material is undergoing. Also, the material could be used to replace toxic dyes used in the textile industry. Not only are the polymer opals non-toxic, their colors don’t fade or run. Imagine garments that go way beyond Hypercolor t-shirts and Marty McFly’s cap in Back To The Future II.
Additionally, the technology is also being courted as a cheaper alternative to the counterfeit-proof holograms on some banknotes. The University of Cambridge is currently looking for industrial partners to commercialize the polymer opals.
Credit: University of Cambridge