Confining Atoms in a Small Tube Creates a Strange “Primary Gas”

The krypton atoms become stuck in a “traffic jam” inside the carbon nanotube, unable to pass through each other, allowing scientists to more easily observe how the krypton atoms interact. Researchers hope that this “primary energetic body” can shed light on fundamental physical forces.

Andrey Klobistov and his colleagues at the University of Nottingham, UK, have discovered that the narrow space restricts movement and makes it easier to observe the inside of carbon nanotubes, which are just 1.5 nanometers thick (one-half millionth the width of a human hair). He spent years studying chemical reactions. They have now developed a way to do the same thing with atoms of the rare gas krypton, creating a so-called one-dimensional gas.

The researchers used a buckminsterfullerene molecule, a spherical cage made of 60 carbon atoms, with a krypton atom trapped inside. These molecules are sucked into the carbon nanotube by van der Waals forces, weak attractive forces caused by fluctuations in the electron cloud surrounding the atomic nucleus. Once filled, the tube is heated to 1200 °C and the cage is destroyed. The carbon atoms are absorbed into the nanotube, leaving behind a string of krypton atoms.

Klovistov said the result is like a “traffic jam” in which atoms can be observed slowly, rather than flying around at up to 400 meters per second, as they often do in three-dimensional gases. The group used a transmission electron microscope to image atoms, allowing them to accurately measure the distances between them.

“They fundamentally change their behavior,” Klovistov said. “This is a very interesting system. We can track their trajectories, how they move and how they interact. This is a great toy to play with with noble gases. “We can gain a fundamental understanding of the behavior of atoms under extreme confinement.”

Other researchers have already observed that krypton atoms form pairs held together by van der Waals forces. This phenomenon is difficult to observe in unconstrained atoms and can also occur within nanotubes. Klobistov said future experiments will be “full of surprises.”

Future research will investigate how temperature affects primary gas. If you reduce the temperature of a gas in three-dimensional space, it will condense into a liquid and then solidify, but there is no guarantee that the same rules will apply in his one dimension.

“Maybe there's no such thing as a 1D liquid, it's just a 1D solid. It's a bit of a voyage of discovery,” says Klobistov.