By adding a polymer acid to a common plastic, chemists at the University of Texas at Austin have developed a new kind of plastic material that features changeable conductivity. The "doped" plastic technology could be used to provide cheap, flexible wiring in future electronics products, says Yueh-Lin Loo, the assistant professor of chemical engineering whose laboratory developed the process.
The chemically altered polyaniline, which Loo says can be easily manufactured, offers conductivity up to 10 times higher than non-doped plastics. Flexible plastic sheets created in the lab can be printed with wires and interconnects that can be used to design products such as military camouflage coverings, foldable electronic displays, and environmental sensors.
Compared to Loo's plastic alternative, conventional metal wires made out of gold, copper, or silver are both expensive and difficult to manufacture. The new polyaniline/polymer acid material, on the other hand, can be produced at room temperature and without costly manufacturing hardware, such as vacuum chambers.
The plastic also offers the benefit of being able to change color in accordance with its conductivity. This characteristic could lead to an array of color-changing business and consumer electronic devices. "\[The plastic\] absorbs wavelengths of light at different regions; it's inherent in the nature of the material," Loo says. "Its overall versatility could lead to the development of many new products."
Although the doped-plastic offers up to a tenfold conductivity increase over its non-doped counterparts, the material still doesn't come close to copper wiring's ability to conduct electricity. "We're still a couple of orders of magnitude off from copper," Loo says. "They're still conductors, but not like the copper or gold wiring that we're used to."
Despite the material's inferior conductivity, Loo sees a bright future for polyaniline connections in flexible electronics, where the material's low cost, light weight, and extreme pliancy can't be matched by metal wires. "Because they're polymers, they can be flexible and they're easily processable," says Loo. These characteristics would make plastic wiring a good choice for use in products ranging from disposable electronic devices to digital posters.
The technology could also find a home in sensing devices. "You can use the changing color to sense changes in the environment," says Loo. "If you expose it to a certain chemical, \[the material\] changes its structure. It no longer becomes conductive, and then you see a change in the color."
Loo and her colleagues are still struggling to understand exactly why the material behaves the way it does. So far, they have learned that higher-mass acids attach to the plastic in longer chains and induce a less ordered internal structure within the plastic. "But we still don't quite understand why our conductivities are high relative to other conductive polymers out there," Loo says. "Our next stage will be to investigate this."
Loo says that key to the future research will be finding a way to raise conductivity to a level that will make plastic wires useful over longer distances. "We've made transistors using polyaniline source and drain electrodes instead of gold and copper, and they work beautifully," she says. "But when you make them into a circuit, and your polyaniline wire is long, you have a large resistance drop along the wire."
If the additional research poses no big surprises, Loo expects polyaniline wiring to become a commercial technology within the next five to 10 years. She notes that the material's simple production requirements make it relatively easy to experiment with different formulas. "The beauty of this is that we can make this \[material\] in house," she says. "So we know exactly what we put in and we know exactly what we're making."