Up to now, scientists have believed that plastics require ordered polymer chains in order to be able to conduct electricity, but a study by researchers from Linköping University and Stanford University has revealed that this is not necessarily the case. The study is reported in a paper in the Proceedings of the National Academy of Sciences (PNAS).
There has been a lot of development in polymers since the phenomenon of conducting and semi-conducting plastics was first discovered, resulting in a Nobel Prize in 2000. Their weakness is still speed: plastics conduct a charge slowly, compared to silicon for instance, although advances are continually being made.
”The charge is transported two to three times faster in the latest generation polymers,” explains Simone Fabiano, researcher in the Laboratory of Organic Electronics at Linköping University and lead author of the PNAS paper.
In order to increase conductivity, scientists have focused on getting the polymer chains to be as well ordered as possible. The idea is that it should be easier for the charge to jump between the chains if they are organized in rows. Fabiano compares the polymer chains to spaghetti: they should line up next to each other, rather than being all tangled up.
To their surprise, however, the researchers observed during their experiments that the charge seems to travel as quickly in an unordered polymer as in an ordered, crystalline one. Further research revealed that crystallinity, or the degree of structural order in a solid, actually does not play a part in how quickly a polymer conducts.
”We see that the new generation of polymers has such small defects that the charge moves faster along the chain instead of jumping between the chains,” says Fabiano. “For the charge carrier, it takes less energy to travel along the chain than to jump to the adjacent one. So the polymer is a faster conductor.”
The ideal situation seems to be for the polymer to possess some a degree of disorder and for the polymer chains to aggregate from time to time, making it easier for the charge to jump between them.
Fabiano is now turning to chemists to implement his findings. ”It is about design at the molecular level,” he explains. “That they can continue to reduce the defects and focus on enabling the polymer chains to make better contact with each other, rather than forming large crystalizing order.”
This story is adapted from material from Linköping University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.