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Team Focuses on Coating Color Changes

Monday, November 28, 2016

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New coatings could produce a range of colors based on nanostructures rather than pigments, says a group of researchers at work on a thin, scratch-resistant coating they say “could be a real revolution.”

The team, led by Harvard University’s Henning Galinski and including researchers from King Abdullah University of Science and Technology (Saudi Arabia) and ETH Zurich (Switzerland), released its findings in the journal Light: Science & Applications.

Plum Throated Cotinga
© Dušan M. Brinkhuizen via Cornell Lab of Ornithology Neotropical Birds Online

Structural coloration is how we see color in some plant materials, insects, and birds like the plum-throated cotinga (pictured), which served as an inspiration for the researchers on the coating project.

It’s not the first research foray into color-changing coatings, or the underpinning idea, which is called structural coloration, but the team says it’s a major step toward scalable versions of the technology, which could have applications from buildings to cars and airplanes.

Structural Coloration

The idea of structural coloration involves biological nanostructures that allow seemingly colorless materials to reflect light in ways that create a colorful appearance—that is, color that’s in the structure itself, rather than a pigment or dye. It’s how we see color in some plant materials, insects, and birds like peacocks or the plum-throated cotinga, which served as an inspiration for the researchers on the coating project.

The new development, according to King Abdullah University, involves spraying a platinum-aluminum alloy onto the substrate, then “dealloying,” removing most of the aluminum and ultimately combining “dealloyed subwavelength structures at the nanoscale with loss-less, ultra-thin dielectrics coatings.”

Sapphire Controls Hue

The coating starts out transparent. Then, an ultra-thin layer of sapphire is infused into the coating. Sapphire is an especially hard mineral, already used in glass to make scratch-resistant windows and screens for electronics. The sapphire lends hardness and abrasion-resistance to the coated surface, and also engenders the color-shifting abilities of the coating.

The thickness of the sapphire determines the color the coating takes on, because the sapphire particles fill “nanopores” in the coating in different ways at different thicknesses. Changing the thickness of the layer at the nano scale can generate any desired color, and because the coloration is part of the material structure, it won’t fade.

'Programmed' Color

Unlike recent developments in coatings that could change color on demand, the coating isn’t ever-changing. It can, however, be tailored to any color needed, without pigments or additives; the color can be “programmed” into the coating as it is applied, meaning one batch of coating material could create any number of colors using the same process.

Because the coating is thin, durable and can produce any color on demand, it could be used for architectural applications and beyond. The researchers say the technology could find a place in the automotive recoat industry, or even aerospace coatings.


Tagged categories: Aerospace; Asia Pacific; Automotive coatings; Coating Materials; Coatings Technology; Colleges and Universities; Color; EMEA (Europe, Middle East and Africa); Fade-Resistant Color; Latin America; Nanotechnology; North America; Research

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