Michael Miller and Tricia CarmichaelPhD student Michael Miller, left, and chemistry professor Tricia Carmichael examine a piece of silicone rubber with silver nanowires embedded in it. Their method of making the prototype marks an important step towards making stretchable electronics a reality.

Chemists develop innovative method for making bendable electronics

A chemist and her team of researchers have made a major stride forward in the race to make cell phones, televisions and other electronics that can bend and stretch.

Tricia Carmichael, an associate professor in chemistry and biochemistry, and her PhD student Michael Miller, are two of five co-authors on a recently published paper describing a process that uses tiny silver nanowires as conductors and then arranging and mixing them right in to the adhesive that bonds them to surfaces like the plastic which could be used in bendable electronic devices.

“Glues are really durable material, so it made sense to do it that way,” Dr. Carmichael said of the never-before-used process described in the academic journal Applied Materials and Interfaces. “We wanted it to be general enough that it could be used by everyone in the industry. It’s just really practical.”

Until now, manufacturers have relied on indium tin oxide as a conductor in electronic light-emitting displays, but it’s completely unsuitable for flexible devices because it’s a brittle ceramic which cracks under relatively low bending strains and causes electrical failure.

Silver nanowires provide a possible alternative, but they don’t adhere well to certain surfaces and individual wires often protrude out beyond the 100 nanometre guideline that’s standard for thickness used in most electronic devices.

The Carmichael lab’s process involves pouring the silver nanowires from the liquid solution they’re contained in on to a filter paper so they form in a film, a continuous pathway that can conduct electricity. Those films are then peeled off and heated so they bond together. Then they’re mixed with an adhesive and “sandwiched” between two layers so that they bond to such surfaces as flexible polyethylene terephthalate (PET) plastic or elastomeric polydimethylsiloxane (PDMS), both substrates which could be used in flexible electronic devices.

“We can control which piece of “bread” we want the nanowire formation to adhere to by modifying the surface chemistry, depending on what it’s made of,” Carmichael explained. “We use an oxidation process to do that.”

Miller said the simple-but-brilliant idea to mix the nanowires in with the adhesive actually came from another unrelated project that was being done in the lab.

“We took what we knew and applied it to this project and it worked the first time,” said Miller, who will defend his thesis next month. “That’s actually quite rare. Lots of people are working with silver nanowires, but no one has ever thought to actually mix them right in with the adhesive.”

The team actually built a prototype organic light-emitting device just to demonstrate that the process works in principle. In order for it to work in a real device, however, it would need to be scaled up and proven able to illuminate individual pixels, Miller said.

Carmichael will appear today on Research Matters, a weekly talk show that focuses on the work of University of Windsor researchers and airs every Thursday at 4:30 p.m. on CJAM 99.1 FM.

Listen to the show:

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