Electronic Friction

Illustration of a carbon nanotube.

Years ago, physicists discovered that water flows with surprisingly little friction through narrow carbon nanotubes. At our scale, flow behavior is typically the opposite: there’s greater friction (and, thus, slower flow) in a narrower pipe. To unravel the mystery, researchers had to delve into quantum mechanics and model the interactions between the atoms of a water molecule and the electrons of the carbon atom. Essentially, this meant building a quantum picture of the liquid-solid interface inside the nanotube.

The team found that the electrons of the nanotube exert a drag-like force on the water molecules, creating friction that slows the flow. Since narrow nanotubes have fewer electrons than larger tubes, there is less friction on the flow and the water flows faster! (Image credit: cintersimone; research credit: N. Kavokine et al.; via SciAm; submitted by Kam-Yung Soh)

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