Sunday, October 25, 2015

Windsor Research Spotlight - Stretching the Limit

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 This link will take you to another Web site ACS Applied Materials & Interfaces

To see the original story on the NSERC web site, click here.

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