A new plastic-like material that behaves like metal

A new plastic-like material that behaves like metal

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A group of researchers at the University of Chicago has found a way to make a material in which the molecular fragments are mixed and disordered (like plastic), but which can still conduct electricity very well. This advance could pave the way for a new class of materials, robust and easily shaped, for electronics and many everyday devices.

If all materials do not have the same physical properties, it is because of their atomic structure. So-called “organized” (or crystalline) materials such as metals consist of atoms, ions or molecules arranged regularly in networks. In “amorphous” materials such as glass, the atoms have no particular organization. Finally, the polymers that make up plastic materials are linked together, in a linear or branched fashion.

Among other properties, its conductivity is determined by the internal structure of the material. Metals (silver, copper, gold, aluminum, etc.) are the oldest and most important group of conductors. However, a few decades ago, scientists managed to create conductive materials from organic materials; in addition, they add small amounts of “impurities” to said material – a process called “doping”. These doped materials are more flexible and easier to process than traditional metals, but they are much less stable and can lose conductivity under certain conditions.

An efficient and particularly robust controller

These conductive organic materials — doped organic polymers, but also molecular conductors and new coordination polymers — are the basis of many technologies, from screens to flexible electronics. Doping allows atoms and molecules to be “arranged” into a well-organized network, as in a metal, so that electrons can circulate easily through the material.

Scientists have always thought that a material must necessarily have an ordered atomic structure in order to conduct electricity effectively. ” Even organic materials that are inherently conductive, such as single-component molecular conductors, must be crystalline to behave metallically. “, note the researchers in Nature. However, their discovery challenges this principle.

Illustration of material structure. Nickel atoms are shown in green, carbon atoms in gray and sulfur atoms in yellow. © Xie et al.

Jiaze Xie, a researcher in the Department of Chemistry at the University of Chicago, decided to conduct new experiments with an amorphous coordination polymer: nickel tetrathiafulvalene tetrathiolate. Basically, it is a polymer made up of nickel atoms strung like pearls on chains made up of carbon and sulfur atoms.

Not only did the material conduct electricity easily and strongly (up to 1200 S/cm), but it proved very stable in moist air for weeks, at pH 0 to 14, and at temperatures ranging up to 140°C. ” We heated it, cooled it, exposed it to air and moisture, even poured acid and alkali over it and nothing happened. », Xie said. This rock-solid robustness would obviously be very useful for real-world applications.

A discovery that multiplies the possibilities of the electronics industry

These results show that molecular design can enable metallic conductivity even in highly disordered materials, raising fundamental questions about how metallic transport can exist without periodic structure, the researchers write. The molecular structure of the material really surprised Xie and his team. ” Fundamentally, it should not be able to be a metal. There is no solid theory to explain this said John Anderson, associate professor of chemistry at the University of Chicago and lead author of the study.

How could this material conduct electricity when in theory it couldn’t? After several tests, computer simulations and theoretical work, scientists believe that this material forms layers like sheets of lasagna; the team mentions “a particularly robust molecular overlap” in their paper. Even if these sheets tilt to the side and the stack is no longer truly ordered, the electrons can still move horizontally or vertically if the layers are connected together.

This new conductive material thus offers unprecedented possibilities and paves the way for a fundamentally new design principle for electronic technology. ” It’s almost like conductive dough: you can put it in place and it conducts electricity Anderson said.

One of the interesting features of this material is that it offers new processing possibilities: unlike metals, which generally have to be melted down to get the right shape — which means other parts of the device have to withstand very high heat — this new material can be shaped at room temperature temperature. It can also be used in virtually any environment – ​​where heat, acidity, alkalinity or humidity previously limited design options.

Xie and her team are now exploring the different forms and functions the material could have. In particular, they plan for it to be two- or three-dimensional and to be porous, among other features.

source: J. Xie et al., Nature

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