When hurt, self-healing plastics
turn red
Could
be ideal for airplanes that fix themselves in flight, to cars with parking-lot
scratches
A new genre of plastics can mimic
the human skin's ability to heal scratches and cuts. This small patch of
plastic turns red when damaged but heals
itself when exposed to light .
Scientists are creeping closer to
the creation of self-healing plastics full of sci-fi features that would be
ideal for everything from airplanes that fix themselves in flight to cars whose
parking-lot scratches disappear by the end of the day.
In one of the latest developments,
researchers are reporting a material that changes color when compromised and
then self-heals in response to light or other stimuli.
While many of the details are
industry-guarded secrets, each step forward brings companies closer to creating
a new generation of products that retain their integrity indefinitely.
“There are millions and millions of
applications, ranging from transportation to sensing to space to energy to
cosmetics to health to medicine to many things,” said Marek Urban, a polymer
scientist at the University of Southern Mississippi in Hattiesburg, who
presented some of his latest work today at a the American Chemical Society
meeting in San Diego. “Whatever you desire.”
One of the first major breakthroughs
in self-healing materials came in 2001, when researchers at the University of
Illinois at Urbana-Champaign figured out how to embed microcapsules into
polymers. These long chains of repeated molecular units are linked with
chemical bonds. When the material was damaged, the microcapsules would break
open, releasing a liquid healing agent that would repair broken bonds.
Scientists have made a number of
technical advances since then, including refinements in how quickly and
efficiently chemical bonds can be disassembled and reassembled within
materials.
Although the new generation of
coatings is often called “self-healing,” most of these materials don’t actually
heal themselves, said Christoph Weder, a polymer scientist at the University of
Fribourg in Switzerland. Instead, something is required to stimulate healing.
Early generation versions required heat to essentially melt molecules and allow
them to flow back together.
In 2009, Urban’s team developed a
polyurethane polymer that healed with exposure to ultraviolet light. And last
year, in a paper that appeared in the journal Nature, Weder and
colleagues reported the use of focused UV light to spark the healing process in a different kind of
rubbery plastic that is made of shorter molecules and linked with metal ions.
Urban’s team has now developed
self-heating latex coatings that turn red when damaged, reminiscent of the
blood on a human scratch. Like paint, Urban said, the material can be applied
to just about any kind of surface. Tiny sensing molecules are spaced at regular
intervals throughout the polymer so that when bonds break as a result of damage
to the surface, a color change occurs.
Then, when exposed to specific
wavelengths light or to specific temperature or pH conditions, the molecule
closes back up again. Urban’s new material turns red when damaged, but future
versions will likely use other colors.
“This is the first example of a
material that self heals and also changes color,” he told Discovery News.
“Nobody ever did this before.”
"Mother Nature has endowed all
kinds of biological systems with the ability to repair themselves,"
including skin, DNA and tree bark, Urban added in a press release. "Our
new plastic tries to mimic nature, issuing a red signal when damaged and then
renewing itself when exposed to visible light, temperature or pH changes."
Color changes could be useful
signals that would alert engineers or consumers that damage has occurred to a
product, Weder said. The visible scratch would then guide the application of
light to focus on the area that needs it.
“This is something that has been on
my drawing board for a long time,” Weder said. “It shows you where the defect
is and the system can then be healed.”
Earlier this year in Europe, Nissan
released prototypes of an iPhone case with self-healing technology. But there
is still a ways to go before the technology becomes widespread.
It is relatively easy, for example,
to make soft materials that self-heal, Urban said, because gel-like substances
flow easily. But it is much more difficult to create hard and durable
self-healing materials that can withstand heat and stress, which would be far
more useful in the bolts or coatings of objects like airplanes and space
shuttles.
Some day, Urban said, scientists may
be able to make objects out of materials that replicate and self-heal,
essentially growing like trees.
Marek W. Urban via ACS
By Emily Sohn
http://www.nbcnews.com/id/46861927/#.UnP_olMpfFw
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