Two-dimensional nanomaterial expands counter-intuitively under tension
by Clarence Oxford
Los Angeles CA (SPX) Apr 19, 2024

Expanding material under tension usually results in a decrease in width, similar to inflating a balloon. However, a groundbreaking development by PhD student Noah Stocek and physicist Giovanni Fanchini at Western University exhibits a rare counter-example.

At Interface Science Western's Tandetron Accelerator Facility, Stocek and Fanchini engineered two-dimensional tungsten semi-carbide nanosheets (W2C) that uniquely expand perpendicular to the direction of applied force, a property characteristic of auxetic materials.

Unlike traditional flat structures, these nanosheets are designed with a dimpled, egg carton-like surface. When stretched, the structure causes an outward expansion as the dimples flatten. This phenomenon has been previously recorded in only one other material which expanded by 10 per cent per unit length. The W2C nanosheet developed at Western expands by an unprecedented 40 percent.

"In 2018, theorists anticipated this auxetic behavior in tungsten semi-carbide, but practical development had eluded researchers worldwide," said Stocek.

The creation of these nanosheets wasn't feasible through chemical processes typically employed for two-dimensional materials. Stocek and Fanchini instead utilized plasma physics to assemble the layers, leveraging the fourth state of matter used in technologies ranging from neon lights to flat-screen TVs.

Traditional methods using high-temperature gas reactions in furnaces were ineffective, prompting the researchers to innovate a new method involving electrically charged plasma particles.

Applications for these W2C nanosheets are extensive, starting with a novel strain gauge capable of monitoring structural changes in real-time through conductivity changes.

"This two-dimensional nanomaterial could revolutionize strain gauges, allowing for enhanced monitoring of structures like airplane wings or household pipes," explained Stocek. "Unlike typical gauges, which become less conductive when stretched, our material increases in conductivity, offering new potential in sensors and stretchable electronics."

Research Report:Giant Auxetic Behavior in Remote-plasma Synthesized Few-Layer Tungsten Semicarbide

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