Researchers have shown why deep, pure red colors in nature are mainly produced from pigments, instead of the structural color that produces bright blue and green hues.
The researchers, from the University of Cambridge, used a numerical experiment to determine the limits of opaque structural color, a phenomenon responsible for some of the most intense colors in nature, and found that it only extends to blue and green. the visible spectrum. The results, published in PNAS, could be useful in the development of non-toxic deep-colored paints or coatings that never fade.
The structural color, which is seen in some bird feathers, butterfly wings or insects, is not caused by pigments or dyes, but only by the internal structure. The appearance of the color, whether opaque or iridescent, will depend on how the structures are arranged at the nanoscale.
The ordered, or crystalline, structures produce iridescent colors, which change when viewed from different angles. Cluttered or interrelated structures produce angle-independent matte colors that look the same from any viewing angle. Since the structural color does not fade, these corner independent matte colors would be very useful for applications such as paints or coatings, where metallic effects are not required.
“In addition to their intensity and fade resistance, a matte paint using the structural color would also be much more environmentally friendly, as no toxic dyes and pigments would be needed,”
“Most examples of structural color in nature are iridescent – so far, examples of natural opaque structural color only exist in blue or green shades,” said co-author Lukas Schertel. “When we tried to artificially recreate an opaque structural color for reds or oranges, we end up with a poor quality result, both in terms of color saturation and purity.”
Based in Dr Silvia Vignolini’s laboratory, the researchers used numerical modeling to determine the limits of creating a saturated, pure and opaque red structural color.
The researchers modeled the optical response and color appearance of the nanostructures, as found in the natural world. They found that saturated and opaque structural colors cannot be recreated in the red region of the visible spectrum, which could explain the absence of these hues in natural systems.
“Due to the complex interplay between single and multiple scattering, and the contributions of correlated scattering, we found that in addition to red, yellow and orange can also hardly be reached,” Vignolini said.
Despite the apparent limitations of structural color, the researchers say these can be overcome by using other types of nanostructures, such as network structures or multi-level hierarchical structures, although these systems are still not fully understood.
Structural colors, without reflections
Gianni Jacucci et al, The limits of the extent of the color palette of nature in correlated and disordered systems, Proceedings of the National Academy of Sciences (2020). DOI: 10.1073 / pnas.2010486117
Computational Modeling Explains Why Blue and Green Are the Brightest Colors in Nature (2020, September 11)
recovered on September 13, 2020
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