It is a common hack to stretch a balloon out to make it easier to inflate. When the balloon stretches, the width crosswise shrinks to the size of a string. Noah Stocek, a PhD student collaborating with Western University physicist Giovanni Fanchini, has developed a new nanomaterial that demonstrates 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 semi-carbide (or W2C, a chemical compound containing equal parts of tungsten and carbon atoms) which when stretched in one direction, expand perpendicular to the applied force. This structural design is known as auxetics.
The trick is that the structure of the nanosheet itself isn’t flat. The atoms in the sheet are made of repeating units consisting of two tungsten atoms to every carbon atom, which are arranged metaphorically like the dimpled surface of an egg carton. As tension is applied across the elastic nanosheet in one direction, it expands out in the other dimension as the dimples flatten.
Prior to this innovation, there has been only one reported material that could expand by 10 percent per unit length in this counter-intuitive way. The Western-engineered tungsten semi-carbide nanosheet can expand to 40 percent, a new world record.
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