A newly-developed film made of gold nanoparticles could allow robots to adopt the type of camouflage and skin color properties of creatures such as chameleons and octopi. The material is capable of changing color in response to any type of movement.
The material was created by UC Riverside scientists and it was documented in a paper published in Nature Communications last week.
This material is different from the others that are used to mimic color changing in nature. The film is able to change based on any type of movement, including bending and twisting. This material could be applied to the outside of robots, allowing them to enter into environments that are dangerous or even impossible for humans.
Some of these environments could include places like underwater crevices that are extremely hard to enter. Another one of the possible benefits of this material is that biologists could use it to learn about animals in these environments and the pressures they face.
There are other materials that have color-changing properties based on motion, but the film of gold nanoparticles is able to be printed and programmed to display complex patterns.
Nanomaterials and Magnets
Nanomaterials are materials that have been reduced to be extremely small. They can be the size of a virus, which is about tens of nanometers in width and length. There are some specific materials, such as silver and gold, that have color-changing properties based on size, shape, and the direction they face.
“In our case, we reduced gold to nano-sized rods. We knew that if we could make the rods point in a particular direction, we could control their color,” said Yadong Yin, a chemistry professor. “Facing one way, they might appear red. Move them 45 degrees, and they change to green.”
One of the challenges for the research team was to get millions of gold nanorods to float in a liquid solution, as well as getting them all to point in the same direction and display a uniform color.
To get around this, the team took the larger gold magnet nanorods and fused smaller ones onto them. The pair was then encapsulated in a polymer shield to keep them side-by-side, and then magnets were able to be used in order to control the orientation of both of the rods.
“Just like if you hold a magnet over a pile of needles, they all point in the same direction. That's how we control the color,” Yin said.
The nanorods are dried into a thin film and stop responding to magnets after their orientation is fixed in place.
“But, if the film is flexible, you can bend and rotate it, and will still see different colors as the orientation changes,” Yin said.
Futuristic Robots and Currency Authentication
The main goal is to use this material on futuristic robots, but there are other applications as well. According to UC Riverside chemist Zhiwei Li, who is the first author of the paper, the film can be used in checks or cash and act as an authentication feature. Whenever the film is exposed to normal lighting, it is gray, but through the use of polarized lenses, elaborate patterns show up. Movement such as twisting can also change the color contrast of the film.
The research team sees an endless amount of applications.
“Artists could use this technology to create fascinating paintings that are wildly different depending on the angle from which they are viewed,” Li said. “It would be wonderful to see how the science in our work could be combined with the beauty of art.”