It is a common practice to stretch a balloon to make it easier to inflate. As the balloon stretches, its horizontal width decreases to the size of the string. Noah Stocek, a PhD student at Western University in collaboration with physicist Giovanni Fanchini, developed the following new nanomaterials: the opposite of this phenomenon.
Working at Interface Science Western, home of the Tandetron Accelerator Facility, Stocek and Fanchini formulated two-dimensional nanosheets of tungsten torcarbide (or W2C, a compound containing equal parts tungsten and carbon atoms). These nanosheets expand when stretched in one direction. Perpendicular to the applied force. This structural design is known as auxetics.
The problem is that the structure of the nanosheet itself is not flat. The atoms in the sheet are made up of repeating units of two tungsten atoms for every carbon atom, metaphorically arranged like the dimpled surface of an egg carton. When tension is applied across the elastic nanosheet in one direction, the dimples flatten and the tension extends into other dimensions.
Before this innovation, only one material had been reported that could scale up to 10% per unit length in this counterintuitive manner. Western-designed tungsten torcarbide nanosheets can scale up to 40%, a new world record.
“We were specifically looking for a way to make two-dimensional nanomaterials from tungsten torcarbide,” Stocek said. “In 2018, theorists predicted that this behavior would emerge at extraordinary levels, but despite extensive attempts by research groups around the world, no one has been able to develop it.”
Because it was impossible to create the new tungsten torcarbide nanomaterial using chemical means, Stocek and Fanchini relied on plasma physics to form single atomic layers. Plasma is made up of charged particles of atoms and is the fourth state of matter (solid, liquid, gas). Plasma can be observed in nature through the Northern Lights, the Aurora Borealis, and the Sun's corona during a recent solar eclipse. It is also used in neon lighting, fluorescent lighting, and flat-screen TVs.
Typically, the devices used to create two-dimensional nanomaterials are specialized furnaces that heat gases to temperatures high enough to chemically react to form the desired materials. This approach did not work because the most common process, a chemical reaction, produces products that are different from the desired nanomaterial.
“Most researchers who tried to get this material before us got stuck here, so we had to change direction,” Fanchini said.
Rather than heating a gas made of tungsten and carbon atoms in a furnace to produce neutral particles, as can be achieved from solids, liquids or gases, Stocek and Fanchini designed a new custom device that generates a charged plasma. particle.
expand your goals
There are countless applications for these W2C nanosheets, starting with a new type of strain gauge. These commercially available gauges are the standard way to measure expansion and sagging in everything from airplane wings to household plumbing.
“Imagine you want to know if a pipe in your house is deformed and at risk of bursting at any moment. You could attach a sensor to a pipe made of this two-dimensional nanomaterial and then use a computer to monitor the current passing through the pipe. If the current rises, This means the pipes are at risk of expanding and bursting,” Stocek said.
In fact, new nanomaterials are becoming more electrically conductive, opening the door to endless possibilities for their use in sensors or any device that detects events or changes in the environment and transmits information to other electronic devices. Another application is to insert the material directly into stretchable electronic devices, such as wearable technology, to make them more conductive.
“Typically, strain gauges rely on the fact that when you stretch a material, it becomes thinner and the conductivity of the material changes to carry an electric current,” Fanchini said. “With these new nanomaterials, that won’t happen anymore.”