Color-changing coatings ready for the big time

November 21, 2016, King Abdullah University of Science and Technology

Wafer-thin, scratch-proof films can generate a rainbow of colors using random metallic nanostructures.

The dazzling colors of peacock feathers arise from the physical interaction of light with biological nanostructures. Researchers have discovered how to exploit this natural trickery known as structural coloration into a large-scale printing technology that produces lightweight and ultra-resistant coatings in any color desirable.

Researchers routinely produce photonic structures to influence the behavior of light for applications such as fiber-optic communications. Many groups have used photonic technology to generate new forms of artificial structural colors that take advantage of the entire spectrum of visible light.

Moving this technology out of the lab is challenging, however, because are often fragile and difficult to produce in practical quantities.

Andrea Fratalocchi from the University's electrical engineering program and colleagues from Harvard University and ETH Zurich used wet chemical techniques to help overcome the difficulties of scaling-up photonic colors. Inspired by the nanoporous feathers of the plum-throated cotinga bird, the team's approach began by sputtering a platinum-aluminum based alloy on to a target surface. Then, a process called dealloying dissolves most of the aluminum and causes the remaining metal to reorganize into a bumpy network featuring open nanopores.

Next, the researchers deposited an ultra-thin layer of protective sapphire on to the metal network to both protect the surface and modify the way in which light interacts with the photonic nanopores. Surprisingly, slight changes of the sapphire thickness from 7 to 53 nanometers yielded remarkable color changes-the initially transparent film underwent stepwise transitions to yellow, orange, red and blue tones.

"Controlling these colors is experimentally very simple and uses coating technologies that are cheap and easily implemented," said Fratalocchi. "However, understanding how the complex light-matter interactions generate colors took months of work."

The team's high-level simulations determined that color generation begins when light strikes the metal and generates wave-like entities known as surface plasmons. As the plasmons interact with the randomly distributed pores, they become trapped and modulations in the coating's refractive index produced epsilon-near-zero regions in the nanopores where waves propagate extremely slowly. Adding the sapphire film caused additional reflections of the trapped waves, which created a flow of saturated color through resonance effects.

Fratalocchi noted that the way are formed in this structure can open the way for "programmable" nanomaterials for many applications.

"Imagine a scratch on a car that can be repainted with an extremely thin material without other expensive procedures, or as a lightweight, maintenance-free way to coat airplanes," he stated. "This technology could be a real revolution."

Explore further: Microscopic analysis of blue tarantula inspires production of nanostructures

More information: Scalable, ultra-resistant structural colors based on network metamaterials. DOI: 10.1038/lsa.2016.233

Related Stories

The Unusual Origin of Peacock Brown

June 28, 2005

Many animals' colors originate from photonic crystals, which reflect specific colors of light as a result of their nanoscopic structures, rather than from pigments, which derive their colors from their chemical composition. ...

Aluminum nanoparticles could improve electronic displays

January 6, 2016

Whether showing off family photos on smartphones or watching TV shows on laptops, many people look at liquid crystal displays (LCDs) every day. LCDs are continually being improved, but almost all currently use color technology ...

Recommended for you

Atomic-scale ping-pong

June 20, 2018

New experiments by researchers at the National Graphene Institute at the University of Manchester have shed more light on the gas flow through tiny, angstrom-sized channels with atomically flat walls.

Chameleon-inspired nanolaser changes colors

June 20, 2018

As a chameleon shifts its color from turquoise to pink to orange to green, nature's design principles are at play. Complex nano-mechanics are quietly and effortlessly working to camouflage the lizard's skin to match its environment.

Method could help boost large scale production of graphene

June 19, 2018

The measure by which any conductor is judged is how easily, and speedily, electrons can move through it. On this point, graphene is one of the most promising materials for a breathtaking array of applications. However, its ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.