Focus on pigments: Structural colour to achieve weight savings

As the coatings industry is aware, creating a lighter paint significantly helps to reduce carbon emissions. Now, two scientists from Kobe University in Japan have developed a lighter-weight substance that may reduce the weight of planes and, ultimately, have a huge impact on the amount of fuel used and carbon dioxide produced

Published in ACS Applied Nano Materials, a new paper by Fujii Minoru and Sugimoto Hiroshi details the discovery of a nanosphere-based ink that can cover a large surface like a plane with a light colour, but can be applied more thinly while using 10% of the weight of a conventional paint. The substance is composed of almost-invisible silicon crystals that gains its efficiency by reflecting light as a vibrant colour over the total surface; artists use the same kind of structural colouration to get the whitest of white paint. Per the paper, the new paint’s “high reflectance despite the small coverage is due to the very high scattering efficiency” of its nanoscale structure.

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Kobe University reports that Fujii and Sugimoto’s experimental process article emphasised structural colour over pigment colour. As the article notes, while a pigment swallows specific wavelengths, reflecting back the remainder as visible light, structural colours “arise when light is reflected from parallel nanostructures set apart at just the right distance so that only light of certain wavelengths will survive while others are cancelled out, reflecting only the colour we see.” Examples occur in nature: The wings of butterflies and the feathers of birds of paradise get vibrant colours from the same kinds of structures. Unlike most pigments, structural colour also doesn’t degrade over time.

Air travel has a substantial carbon footprint. Since heavier planes require more fuel to elevate, this new lightweight paint could reduce the environmental impact of flight. As Sugimoto explains, “We can apply it to the coating of, for example, airplanes. The pigments and coatings on an airplane have a weight of several hundreds of kilograms. If we use our nanosphere-based ink, we might be able to reduce the weight to less than 10% of that.”