Illinois University scientists have found a way to use polymer printing to stretch and flatten twisted molecules so that they conduct electricity better.
Conjugated polymers are formed by merging electron-rich molecules along a backbone of alternating single and double chemical bonds.
This conjunction allows electricity to travel very quickly through a polymer, making it highly desirable for use in electrical and optical applications.
Nevertheless, such polymers tend to contort into twisted spirals when they join, severely impeding charge transport.
“The flatness or planarity of a conjugated polymer plays a large role in its ability to conduct electricity,” says team lead and chemical and biomolecular engineering professor, Ying Diao.
“Even a slight twist of the backbone can substantially hinder the ability of the electrons to delocalize and flow.”
Though conjugated polymers can be flattened by applying an enormous amount of pressure or by manipulating their molecular structure, both these techniques are very labor-intensive, opines Diao.
It was postdoctoral researcher Kyung Sun Park and graduate student Justin Kwok who noticed that polymers go through two distinct phases of flow during printing.
The first phase occurs when capillary action pulls on the polymer ink as it begins to evaporate; the second phase is the result of the forces imposed by the printing blades and substrate.
Park and Kwok also uncovered another phase that occurs during printing in which the polymers appear to have vastly different properties, mentions Diao:
“This third phase occurs in between the two already-defined phases, and shows the polymers being stretched into planar shapes.”
According to Diao, not only are the polymers stretched and flattened in this third phase, but they also remain that way after precipitating out of solution.
This helps in fine-tune the printer settings to produce conjugated polymers for use in new, faster biomedical devices and flexible electronics.
“We are discovering a whole zoo of new polymer phases, all sensitive to the forces that take place during the printing process,” intones Diao.
“We envision that these unexplored equilibria and flow-induced phases will ultimately translate into new conjugated polymers with exciting optoelectronic properties.”
Image and content: L. Brian Stauffer/University of Illinois via Eurekalert