A project part-supported by DARPA could see the introduction of dynamic camouflage that has been inspired by the flashing colours of the neon tetra fish.
The team at North Carolina State University (NC State) can change the colour of a material by manipulating the orientation of nanostructured columns in the material.
“Neon tetras can control their brightly coloured stripes by changing the angle of tiny platelets in their skin,” said Chih-Hao Chang, an associate professor of mechanical and aerospace engineering at North Carolina State University (NC State) and corresponding author of a paper on the work.
“For this proof-of-concept study, we’ve created a material that demonstrates a similar ability,” said Zhiren Luo, a PhD student at NC State and first author of the paper. “Specifically, we’ve shown that we can shift the material’s colour by using a magnetic field to change the orientation of an array of nanocolumns.”
According to NC State, the colour-changing material has four layers: a silicon substrate is coated with a polymer that has been embedded with iron oxide nanoparticles. The polymer incorporates a regular array of micron-wide pedestals. The middle layer is an aqueous solution containing free-floating iron oxide nanoparticles, which is held in place by a transparent polymer cover.
When a vertical magnetic field is applied beneath the substrate, it pulls the floating nanoparticles into columns, aligned over the pedestals. By changing the orientation of the magnetic field, researchers can change the orientation of the nanoparticle columns. Changing the angle of the columns shifts the wavelength of light that is most strongly reflected by the material. “For example, we were able to change the perceived colour of the material from dark green to neon yellow,” Luo said.
“You can change the baseline colour of the material by controlling the array of the pedestals on the polymer substrate,” Chang said in a statement. “Next steps for us include fine-tuning the geometry of the column arrays to improve the purity of the colours. We are also planning to work on the development of integrated electromagnets that would allow for more programmable colour shifts.”
As well as camouflage, the researchers are working toward developing applications that include reflective displays.
The paper, “Magnetically Actuated Dynamic Iridescence Inspired by the Neon Tetra,” is published in ACS Nano. The paper was co-authored by Benjamin Evans of Elon University. The work was carried out with support from DARPA and the US National Science Foundation.