Models Present a New View of Nanoscale Friction
An atom-level view of the nanoscale interface between amorphous carbon and diamond. At such a small scale, the surfaces are rough, although researchers have been treating them as smooth.Image source: University of Wisconsin-Madison
To understand friction on a very small scale, a team of University of Wisconsin-Madison engineers had to think big. Friction is a force that affects any application where moving parts come into contact; the more surface contact there is, the stronger the force. At the nanoscale—mere billionths of a meter—friction can wreak havoc on tiny devices made from only a small number of atoms or molecules. With their high surface-to-volume ratio, nanomaterials are especially susceptible to the forces of friction. Yet, researchers have trouble describing friction at such small scales because existing theories are not consistent with how nanomaterials actually behave. Through computer simulations, the group demonstrated that friction at the atomic level behaves similarly to friction generated between large objects. Five hundred years after Leonardo da Vinci discovered the basic friction laws for large objects, the UW-Madison team has shown that similar laws apply at the nanoscale. Current nanoscale friction theories are based on the idea that nanoscale surfaces are smooth—yet in reality, the surfaces resemble a mountain range, where each peak corresponds to an atom or a molecule. The researchers discovered simple laws of nanoscale friction. They found that friction is proportional to the number of atoms that interact between two nanoscale surfaces. The researchers’ simulations showed that, at the nanoscale, materials in contact behave more like large rough objects rubbing against each other, rather than as two perfectly smooth surfaces, as was previously imagined.
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