Plastic With Adjustable Conductivity Developed

A plastic has been modified so its ability to carry an electrical current can be altered during manufacturing to meet the needs of future electronic devices, such as military camouflage that changes colors, foldable electronic displays and medical sensors.

Yueh-Lin Loo, an assistant professor of chemical engineering at the University of Texas at Austin, modified the plastic called polyaniline because it could serve as flexible, inexpensive wiring in future products. By combining polyaniline with a chemical that gives it conductivity, she discovered she could increase the plastic’s conductivity one- to sixfold based on the version of the chemical added. The results involving the chemical polymer acid were published in the April 7 issue of the Journal of Materials Chemistry.

Yueh-Lin Loo, assistant chemical engineering professor at the University of Texas at Austin, in her lab with students involved in the research to manufacture a plastic with conductive properties. With Loo are students (l-r) James Norman, Joung Eun Yoo and Kwang Seok Lee. Yoo was lead author, and Lee a co-author, of a Journal of Materials Chemistry article in which the laboratory demonstrated up to a sixfold increase in conductivity of polyaniline. (Photos: Caroling Lee)

Chemically altered polyaniline has several advantages over the more commonly used metals, like gold and copper, in devices other than computers. For example, Loo’s previous research has demonstrated that “doped” polyaniline can be manufactured in solution at room temperatures and without vacuum chambers. Producing metal-based wires requires special manufacturing conditions in addition to the high cost of the metals.

Since Loo’s laboratory submitted their research to the journal, they have developed a version of polyaniline whose conductivity is 10 times higher than before. However, that level of electrical conductivity still doesn’t rival that of copper, which is used to produce high-speed interconnections.

Loo bends a silicone stamp used in creating patterns for fabricating polyaniline wires. Her laboratory has found a way to manufacture polyaniline with much greater conductivity.

That effort will be based on the greater understanding Loo has gained of the polyaniline/polymer acid. In the article, graduate student Joung Eun Yoo and other members of Loo’s laboratory began determining how higher-mass versions of polymer acid improve the plastic’s conductivity when the two materials are combined. So far, they have learned that the higher mass acids attach to the plastic in longer chains, and induce a less-ordered internal structure (crystallinity) within the plastic.

“Understanding how the structure of this polyaniline material changes when its conductivity changes will be crucial for selecting the right material for different consumer applications,” Loo said. She noted that the ability of the plastic to change colors depending on whether it was conductive or not could be especially useful. “Its general versatility could lead to a variety of new consumer products in upcoming years,” she said.

A pliable sheet with printed polyaniline wires and interconnects. The electric current of the flexible plastic can be changed, which could lead to its use in the manufacture future electronic devices.

Loo has begun collaborating with research professor Adam Heller at the university to investigate using polyaniline as part of a sensor material in medical devices. Heller previously developed two commercially available devices to monitor glucose levels in people with diabetes.

Loo’s latest published research was funded by a Young Investigator Award she received in 2005 from the Arnold and Mabel Beckman Foundation and by a Dupont Young Professor Grant. Her research also led to her receiving an National Science Foundation CAREER Award in 2004.

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