One of the aims of material scientists is to find new polymer materials that are conductive—or at least to invent ways to improve the electrical conductivity of existing polymers.

Now scientists have discovered a novel way to achieve the latter using polymer printing. A team at the University of Illinois developed a new method to stretch and flatten the molecules in conductive polymers so they can conduct electricity better, researchers said.

The team worked with what are called conjugated polymers, which are formed when molecules rich in electrons meet along a backbone of alternating single and double chemical bonds, they said.

While this union allows electricity to travel very quickly through a polymer—making it a good fit for electrical and optical applications—the polymers themselves tend to contort into twisted spirals when they join, significantly limiting this conductivity.

Researchers realized that if they could solve this issue with these materials, conjugated polymers could be used for electrical applications at a range on par with silicon materials, Professor Ying Diao, who led the research, said in a press statement.

“The flatness or planarity of a conjugated polymer plays a large role in its ability to conduct electricity,” said Diao, a professor of chemical and biomolecular engineering at the university. “Even a slight twist of the backbone can substantially hinder the ability of the electrons to delocalize and flow.”

Professor Ying Diao, left, postdoctoral researcher Kyung Sun Park, seated, and graduate student Justin Kwok have found that twisted polymers can be flattened via the printing process to make them better at conducting electricity. (Image source: L. Brian Stauffer)

Accidental Discovery

There currently are ways to solve the problem, but neither of them are optimal for performance or utility, and both are labor-intensive, Diao said. An enormous amount of pressure can do it, as can manipulating the molecular structure of the materials. However, “there really is no easy way to do this,” she said in the press statement.

It was members of her research team–postdoctoral researcher Kyung Sun Park and graduate student Justin Kwok—who discovered something key to the new method to print the polymers, Diao acknowledged. While running printing experiments and flow simulations in Diao’s lab, they noticed another phase that polymers experience during printing in addition to the two phases already known–a first phase that occurs when capillary action pulls on the polymer ink as it begins to evaporate, and a second that is the result of the forces imposed by the printing blades and substrate.

“Park and Kwok uncovered another phase that occurs during printing in which the polymers appear to have vastly different properties,” Diao said in the statement. “This third phase occurs in between the two already-defined phases, and shows the polymers being stretched into planar shapes.”

Smoothing the Conductive Path

In this phase, the polymers are stretched and flattened, which serves to smooth the path of conductivity, she said. But, more importantly, they remain in this state after precipitating out of solution, Diao said. This latter state enables researchers to fine-tune printer settings to produce conjugated polymers well-suited for biomedical devices and flexible electronics, she said.

“We are discovering a whole zoo of new polymer phases, all sensitive to the forces that take place during the printing process,” Diao said in the press statement.

Researchers published a paper on their work in the journal Science Advances.

The team envisions further exploration of these new phases of polymers during the printing process to optimize conjugated polymers for a range of new applications, Diao said.

This research “will ultimately translate into new conjugated polymers with exciting optoelectronic properties,” she said in the press statement.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco and New York City. In her free time she enjoys surfing, traveling, music, yoga and cooking. She currently resides in a village on the southwest coast of Portugal.