NSERC Research Spotlight - Stretching the Limit
A research team at the University of Windsor has found that working with a problem, instead of against it, can result in incredible breakthroughs. Chemistry professor Tricia Carmichael and co-investigator Heather Filiatrault have successfully created stretchable electronics able to continue conducting electricity even after stretching to the point of cracking.
Stretchable light-emitting devices are the building blocks of foldable and expandable display screens and electronics-integrated clothing, as well as other soft devices designed to go inside a body, like a stretchable balloon catheter that can mend damaged areas of the heart.
“The dilemma with the design of these devices is that when we use electrically conductive materials, like aluminum or copper, these materials will crack when stretched even a minimal amount,” says Dr. Carmichael.
Stretchable electronics integrate a thin film of electrically conductive material with a film of rubber, but the conductive materials crack when they are stretched, which breaks the circuit and renders the device useless.
Carmichael and her lab team investigated the theory that when a rough
surface is stretched it generates multiple micro-cracks, instead of a
few large debilitating cracks. To manipulate the cracking, she simply
added a layer of inexpensive white glue before the thin sheet of metal
was attached.
“Instead of eliminating cracks, we encouraged a lot of cracking, like
a spider web of cracks that don’t form a continuous pathway through the
sheet,” says Carmichael. “The cracks purposefully interfere with each
other, relieving the strain, so the current can flow along a jagged but
continuous pathway.”
The glue layer is watered down to control the film thickness. It is
spread over the rubber layer and creates the required roughness by
forming blobs. Members of Carmichael’s lab built a strain sensor out of
rubber, glue and gold and wrapped it around a thumb. The sensor
successfully monitored when the digit was extended, and when it was not.
Carmichael says this is a low-cost, green solution, which uses simple
components that could potentially scale up to larger surface devices.
“We made the system more defective in order to make it work better,”
she says. “I love this concept of embracing the natural tendency of
cracking, and then pushing it further.”
This research is published as the cover story in the September 30th edition of 
ACS Applied Materials & Interfaces.
To see the original story on the NSERC web site, click here.
Chemistry student Heather Filiatrault and professor Tricia Carmichael examine a light-emitting device fabricated in their lab.
A common method of treating babies born with jaundice is phototherapy, which involves bathing the infant in light from fluorescent bulbs, halogen quartz lamps, light-emitting diodes, and even fiber-optic mattresses.
Tricia Carmichael can see a day when those babies can simply be wrapped in a light-emitting blanket.
An associate professor in chemistry and biochemistry, Dr. Carmichael spends most of her lab time studying ways of making flexible and stretchable electronic devices. In a recent Advanced Materials journal cover article – whose first author was grad student Heather Filiatrault – Carmichael and her colleagues describe an emerging method used to make light-emitting devices designed to tolerate strain so that they can stretch, bend and wrap.
“There are all kinds of cool applications for this technology, but the idea is to be able to make it inexpensively,” Carmichael said.
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The challenge with making stretchable conventional organic light-emitting devices, which rely on technology currently used in cell phones, cameras and digital media players, is the device complexity, Carmichael said. The display screens on those devices consist of thin film layers and each one needs to have an element of elasticity.
Carmichael’s approach has been to reduce the device complexity by using light-emitting electrochemical cells, which rely on materials that give off light when voltage is applied, sandwiched between electrodes. Along with her team, Carmichael developed a way to make a light-emitting material—an organometallic ruthenium complex—stretchable by blending it with an elastic silicone rubber.
“It’s actually a fairly simple idea but no one has ever really done it before,” said Carmichael.
Under lab tests to measure its “stretchability,” the team found the material could achieve about 25 to 30 per cent elongation before the device failed to emit light.
The concept is still in its infancy, but if developed it could have a wide range of potential applications from electronic display signs that could wrap around the corners of buildings to such health applications as light therapy used for healing wounds or activating certain chemotherapy drugs, Carmichael said.
See the original story and a video describing the process on the Daily News:
http://www.uwindsor.ca/dailynews/2012-05-23/chemists-develop-new-method-to-make-stretchable-light-emitting-devices
