UC Riverside scientists have engineered a new nanomaterial that may someday give robots chameleon skin. The novel film is made of gold nanoparticles and changes color in response to any type of movement such as bending or twisting.
Although this may not be the first color-changing material that can also respond to motion, it is the first that can be printed and programmed to display different patterns. The team achieved this film by significantly reducing the size of gold particles.
"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 chemistry professor Yadong Yin. "Facing one way, they might appear red. Move them 45 degrees, and they change to green."
However, the research team was tasked with the difficult goal of taking millions of gold nanorods floating in a liquid solution and steering them all in the same direction to display a uniform color.
To solve this issue, they decided to fuse smaller magnetic nanorods onto the larger gold ones and encapsulate them both in a polymer shield. This ensured that the orientation of both rods could be directed by magnets.
"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.
Best of all, the new material is inexpensive and convenient to make. It can be engineered to coat the surface of any sized object just as easily as applying spray paint.
The research team envisions robotics as the ultimate application of their film but it is by far not the only one. One other useful application can be in the authentication of checks or cash.
When seen through polarized lenses, elaborate patterns emerge on the film that can be used to authentication real cash and checks from fake ones. The film could also be used in art.
"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."