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Plastics future fantastic in prof's view
Pittsburgh Post-Gazette


August 04, 2007

PITTSBURGH -- This is one of Richard McCullough's visions.

In the not-too-distant future, a student will sit down outside a coffee shop, pull a rolled-up plastic sheet out of her backpack, flatten it on the table and immediately be able to read a newspaper, magazine or book of her choice, displayed in glowing colors.

And the whole thing will be made possible by a thin layer of plastics that conduct electricity.

McCullough is a chemistry professor at Carnegie Mellon University and the school's newly appointed vice president of research.

Much of his own lab work over the past 20 years has focused on an unusual class of plastics known as polythiophenes, which conduct electricity well enough to match semiconductors made out of silicon. Someday, he hopes, they will achieve the conductivity of metallic compounds.

What makes the polythiophenes particularly useful is that McCullough and others have figured out a way to make them into inks that can be sprayed or printed onto glass or plastic surfaces in the form of microscopic circuits and electronic components.

Besides the roll-up display sheets, possible uses of these printable conductive polymers include:

-- Organic light-emitting diodes, which have the potential for replacing the liquid-crystal displays used in cell phones, PDAs and most computer and television screens.

-- Solar cells that one day may be more efficient and cheaper than the current silicon-based devices, which could make it commercially feasible to produce electricity from sunlight.

-- Low-cost radio frequency identification tags, or RFIDs, which could be used to track products through their entire life spans, or to prevent counterfeiting of money, CDs or other items.

-- "Smart windows" coated with polythiophenes, which could be tinted to reflect sunlight during warm days, but would turn clear when a current flowed through them, trapping the sun's warmth inside buildings on cold days.

-- Artificial noses that could detect toxic chemicals in a workplace or a war zone, using tiny plastic chips that would change voltage when exposed to certain compounds.

-- Artificial muscles whose plastic strands would contract when a current flowed through them and relax when it stopped.

Conductive polymers were discovered about 30 years ago by the University of Pennsylvania's Alan MacDiarmid, who died earlier this year, along with the University of California's Alan Heeger and Japan's Hideki Shirakawa. They shared the 2000 Nobel Prize in chemistry.

Since then, there have been increasing efforts to turn conductive plastics into innovative products. McCullough has promoted that agenda not only through his academic research, but also by co-founding Plextronics, a fast-growing firm based at the University of Pittsburgh Applied Research Center.

"Our real contribution to this area," he said in a recent interview, "was to bring this material to the masses by providing a method where you can manufacture it in multi-kilogram quantities, dissolve it and turn it into plastics that conduct electricity easily."

He estimated that flexible, all-plastic displays using polythiophenes may be about three to seven years away from production.

"These could be used as maps for the military or displays where you could have your (Pittsburgh) Post-Gazette or New York Times," he said. "The data would be beamed down by satellite through wireless communications to give you your updated version and you could just carry this thing around in your pocket."

For now, he said, the basic circuitry for such displays would have to be etched onto plastic using metallic compounds like indium tin oxide.

But conductive plastics could be used for the semiconductor switches in the circuits, as well as the light-emitting diodes, or LEDs, that would make the displays visible.

Eventually, the displays might include tiny plastic solar cells that would power the devices, eliminating the need for a battery.

Because LEDs are much brighter than the liquid-crystal displays used in most portable devices today, the flexible sheets could easily be read in direct sunlight, he added.

The same basic technology also holds promise for producing the next generation of TV and computer screens, McCullough said.

Because of consumers' thirst for vibrant, high-definition television displays, manufacturers have pushed gas-filled plasma screens. They often produce brilliant pictures, he said, but sometimes have uneven colors, are heavy and don't last that long.

That has pushed several manufacturers to begin working on organic LED displays that will be much lighter and thinner, using conductive plastics, he said.

Both Sony and Toshiba produced prototypes of organic LED flat-panel TV screens this year, and one industry report predicted the market for all such displays will reach $10.9 billion by 2012.

Within the next couple of years, McCullough estimated, single-color polythiophene displays will be available in smaller devices such as cell phones and PDAs. They will also show up in "throwaway" lighting displays on toys, convention message boards and similar items.


Mark Roth can be reached at mroth(at)
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