Members of the Anderson lab at work. Photo: John Zich/University of Chicago.
Members of the Anderson lab at work. Photo: John Zich/University of Chicago.

Scientists at the University of Chicago have discovered a way to create a material that can be made like a plastic but conducts electricity more like a metal. As they report in a paper in Nature, although this material has molecular fragments that are jumbled and disordered, it can still conduct electricity extremely well.

This goes against all of the known rules of conductivity – to a scientist, it’s kind of like seeing a car driving on water and still doing 70mph. But this finding could also be extraordinarily useful; if you want to invent something revolutionary, the process often first starts with discovering a completely new material.

“In principle, this opens up the design of a whole new class of materials that conduct electricity, are easy to shape and are very robust in everyday conditions,” said John Anderson, an associate professor of chemistry at the University of Chicago and senior author of the paper.

“Essentially, it suggests new possibilities for an extremely important technological group of materials,” said Jiaze Xie, a former PhD student at the University of Chicago, who is now at Princeton University, and first author of the paper.

Conductive materials are absolutely essential for making any kind of electronic device, whether it be an iPhone, a solar panel or a television. By far the oldest and largest group of conductors are metals like copper, gold and aluminum. Then, about 50 years ago, scientists were able to create conductors made out of organic materials, using a chemical treatment known as ‘doping’, which sprinkles different atoms or electrons throughout the material. These organic materials are more flexible and easier to process than traditional metals, but the trouble is they aren’t very stable; they can lose their conductivity if exposed to moisture or if the temperature gets too high.

Fundamentally, however, both these organic and traditional metallic conductors share a common characteristic: they are made up of straight, closely packed rows of atoms or molecules. This allows electrons to flow easily through the materials, much like cars on a highway. In fact, scientists thought a material had to have these straight, orderly rows in order to conduct electricity efficiently.

Then Xie began experimenting with materials discovered a few years ago but largely ignored. He strung nickel atoms like pearls along a string of molecular beads made of carbon and sulfur, and began testing.

To the scientists’ astonishment, this material conducted electricity easily and strongly. What’s more, it was very stable. “We heated it, chilled it, exposed it to air and humidity, and even dripped acid and base on it, and nothing happened,” said Xie. That stability is enormously helpful for a device that has to function in the real world.

But to the scientists, the most striking feature of the material was its disordered molecular structure. “From a fundamental picture, that should not be able to be a metal,” said Anderson. “There isn’t a solid theory to explain this.”

Xie, Anderson and their lab worked with other scientists around the university to try to understand how the material was able to conduct electricity. Following tests, simulations and theoretical work, they now think the material forms layers, like sheets in a lasagna. Even if the sheets rotate sideways, no longer forming a neat lasagna stack, electrons can still move horizontally or vertically – as long as the pieces touch.

The end result is unprecedented for a conductive material. “It’s almost like conductive Play-Doh – you can smush it into place and it conducts electricity,” Anderson said.

The scientists are excited because this discovery suggests a fundamentally new design principle for electronics technology. Conductors are so important that virtually any new development opens up new lines for technology, they explained.

One of the material’s attractive characteristics is that it presents new options for processing. For example, metals usually have to be melted in order to be made into the right shape for a chip or device. This limits what you can make with them, since other components of the device have to be able to withstand the heat needed to process the metals.

The new material has no such restriction because it can be made at room temperatures. It can also be used where a device or pieces of a device need to withstand heat, acid or alkalinity, or humidity, which had previously limited engineers’ options for developing new technology.

The team is also exploring the different forms and functions the material might adopt. “We think we can make it 2D or 3D, make it porous, or even introduce other functions by adding different linkers or nodes,” said Xie.

This story is adapted from material from the University of Chicago, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.