Conductive Play-Doh breaks convention

Going against all known rules of conductivity, researchers from the University of Chicago are astonished by a strange material that can be made like plastic but conducts electricity like metal, being likened to conductive Play-Doh.

Conventional electronics, whether it be an iPhone, solar panel, or television, use conductive materials; otherwise, they would be no different than the raw materials they are transformed from.

Metals, such as copper, gold, and aluminum, are by far the oldest and largest group of conductors. Then about 50 years ago, scientists were able to create conductors made of organic materials using a chemical treatment known as doping, which sprinkles in different atoms or "impurities" throughout the material.

The fact that these materials are more flexible and easier to work with than conventional metals is what makes them truly attractive as a replacement to the ancient practices, but the major problem lies in their instability, possibly losing their conductivity if exposed to moisture or if the temperature rises too high.

However, fundamentally, both organic and traditional metallic conductors share a common characteristic – they are made up of straight, closely packed rows of atoms or molecules that allow electrons to easily flow through the material, much like cars on a highway.

Scientists have long thought a material had to have these straight, orderly rows in order to conduct electricity efficiently.

University of Chicago scientists have now dispelled this long-held belief by creating a material that can be made like a plastic but conducts more like a metal – a game-changing discovery that could reshape future electronics.

"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 study published in the journal "Nature."

New class of conductive materials

The research shows how to make a kind of material in which the molecular fragments are jumbled and disordered but can still conduct electricity extremely well.

This goes against all the rules that are currently understood about conductivity – to a scientist, it is kind of like seeing a car driving on water yet whizzing by at 70 miles per hour. But the finding could also prove to be extraordinarily useful. Often, on the way to inventing something revolutionary, the process first starts with discovering a completely new material.

"Essentially, it suggests new possibilities for an extremely important technological group of materials," said Jiaze Xie, first author of the paper published on the discovery.

Experimenting with materials that were discovered years ago but were largely ignored, Xie began to string nickel atoms like pearls into a thread of molecular beads made of carbon and sulfur and started testing.

To his astonishment, and of his colleagues, the material easily and strongly conducted electricity. 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.

These traits are enormously helpful for devices that could potentially function in the real world.

But the most striking thing to the scientists was that the molecular structure of the material was disordered.

"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 can conduct electricity. After tests, simulations, and theoretical work, they think that the material forms layers, like sheets in a lasagna. Even if the sheets rotate sideways, no longer forming a neat stack of pasta, electrons can still move horizontally or vertically – as long as the pieces touch.

The end results are unprecedented for a conductive material.

"It's almost like conductive Play-Doh – you can smush it into place and it conducts electricity," Anderson said.

Opening the floodgates

The researchers are particularly excited about this discovery because it suggests a fundamentally new design principle for electronics technology.

Conductors are so vitally important that virtually any new development opens up new lines for technology, they explained.

One of the material's attractive characteristics is new options for processing. For example, metals must usually be melted to be made into the right shape for a chip or device, which limits what you can make with them since other components of a device have to withstand the heat needed to process these materials.

This new conductive plastic has no such restriction because it can be made at room temperature. Furthermore, it can be used where the need for a device or pieces of the device to withstand heat, acid, alkalinity, or humidity has previously limited engineers' options to develop new technology.

The team is also exploring the different forms and functions the material might make.

"We think we can make it 2D or 3D, make it porous, or even introduce other functions by adding different linkers or nodes," added Xie.

With the possibility to mold a Play-Doh-like conductive material and even attach further characteristics without negating its intrinsic conductivity, the breadth of this material appears limitless at present. Considering the growing popularity of 3D printers, plastic-like filaments that can conduct electricity may be the starting shot that propels us into the next age of electronics.