EVERY school science student learns that plastics don’t conduct electricity,
but the astonishing discovery that some polymers can be made as conductive as
metals has earned three researchers this year’s Nobel Prize in Chemistry. “It’s
a very appropriate piece of work to have received a Nobel prize,” says Richard
Friend of Cambridge University, who works with semiconducting plastics. “It had
a huge impact on the chemistry and physics community.”
Chemists Hideki Shirakawa and Alan MacDiarmid and physicist Alan Heeger were
working together in the 1970s at the University of Pennsylvania on polymers that
had a metallic glint. They modified one such plastic, polyacetylene, by blasting
it with iodine vapour, which gave it a positive charge. To their surprise, its
conductivity increased by a factor of 10 million. The modified polymer’s
conductivity was a match for some metals, although it was still 2000 times less
conductive than copper.
The researchers realised that a polymer with alternating double and single
bonds along its chain of carbon atoms could be made to conduct electricity by
either adding or removing electrons. If you add an electron, it bumps the charge
along the chain from one carbon to the next, creating an electric current.
Removing an electron leaves a “hole” which can also bump along the chain
creating a current (91av, 5 March 1994, p 33). “It seems
obvious now but it was really quite surprising then,” says Friend.
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Researchers predict polymer-based electronics will soon become as ubiquitous
as silicon chips. “I think we’re on the verge of a revolution in polymer
electronics,” says Heeger. “Plastic electronics will be very low cost,” he says,
making them ideal for use in high-volume applications.
Although conducting polymers marked the breakthrough, Friend says the action
has moved on. “The emphasis now is on semiconducting plastics,” he says.
Researchers have used these materials to make plastic transistors and LEDs,
heralding an era of cheap, robust displays that can be rolled up when not in
use. “I’m glad they won and put the focus on this field,” says Ching Tang, a
chemist at Eastman Kodak in Rochester, New York.