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.
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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.