Nanomaterial gives robots chameleon skin
Features include unusual color changes and high touch sensitivity

Date:
June 17, 2020
Source:
University of California - Riverside
Summary:
A new film made of gold nanoparticles changes color in response
to any type of movement. Its unprecedented qualities could allow
robots to mimic chameleons and octopi -- among other futuristic
applications.



FULL STORY ==========================================================================
A new film made of gold nanoparticles changes color in response to any
type of movement. Its unprecedented qualities could allow robots to
mimic chameleons and octopi -- among other futuristic applications.


========================================================================== Unlike other materials that try to emulate nature's color changers, this
one can respond to any type of movement, like bending or twisting. Robots coated in it could enter spaces that might be dangerous or impossible
for humans, and offer information just based on the way they look.

For example, a camouflaged robot could enter tough-to-access underwater crevices. If the robot changes color, biologists could learn about the pressures facing animals that live in these environments.

Although some other color-changing materials can also respond to motion,
this one can be printed and programmed to display different, complex
patterns that are difficult to replicate. The UC Riverside scientists
who created this nanomaterial documented their process in a Nature Communications paper published this past week.

Nanomaterials are simply materials that have been reduced to an extremely
small scale -- tens of nanometers in width and length, or, about the
size of a virus.

When materials like silver or gold become smaller, their colors will
change depending on their 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 chemistry professor Yadong Yin. "Facing one way,
they might appear red. Move them 45 degrees, and they change to green."
The problem facing the research team was how to take millions of gold
nanorods floating in a liquid solution and get them all to point in the
same direction to display a uniform color.



========================================================================== Their solution was to fuse smaller magnetic nanorods onto the larger
gold ones.

The two different-sized rods were encapsulated in a polymer shield,
so that they would remain side by side. That way, the orientation of
both rods could be controlled 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.

Once the nanorods are dried into a thin film, their orientation is
fixed in place and they no longer respond to magnets. "But, if the film
is flexible, you can bend and rotate it, and will still see different
colors as the orientation changes," Yin said.

Other materials, like butterfly wings, are shiny and colorful at certain angles, and can also change color when viewed at other angles. However,
those materials rely on precisely ordered microstructures, which are
difficult and expensive to make for large areas. But this new film can be
made to coat the surface of any sized object just as easily as applying
spray paint on a house.

Though futuristic robots are an ultimate application of this film,
it can be used in many other ways. UC Riverside chemist Zhiwei Li, the
first author on this paper, explained that the film can be incorporated
into checks or cash as an authentication feature. Under normal lighting,
the film is gray, but when you put on sunglasses and look at it through polarized lenses, elaborate patterns can be seen. In addition, the color contrast of the film may change dramatically if you twist the film.

The applications, in fact, are only limited by the imagination. "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."

========================================================================== Story Source: Materials provided by
University_of_California_-_Riverside. Original written by Jules
Bernstein. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Zhiwei Li, Jianbo Jin, Fan Yang, Ningning Song, Yadong Yin. Coupling
magnetic and plasmonic anisotropy in hybrid nanorods for
mechanochromic responses. Nature Communications, 2020; 11 (1) DOI:
10.1038/s41467-020- 16678-8 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200617091022.htm

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