Everybody knows how friction works, right? Rub two things against each other, and they stick together a little, depending on the material. It's why you don't slip around on the sidewalk, unless it's icy, or you're Scooby Doo and you've stepped on a banana peel.
Easy enough – but in fact physics' models of friction leave much to be desired at the atomic level, where (relatively) vast gaps exist between atoms. Most models treat surfaces as relatively continuous "smears" of material, which works reasonably well until you get down to the nanoscale.
However, researchers at the University of Pennsylvania have discovered some interesting properties of friction at the atomic level, which could help engineers improve materials designed to enhance or reduce friction between surfaces.
The researchers have found that friction between two surfaces can be reduced if the surface layers are composed of relatively heavier atoms.
These heavier atoms apparently vibrate at a lower frequency, reducing the amount of energy lost during the sliding process, they say.
The team used an atomic force microscope – an extraordinarily tiny probe which scratches along a surface, a little like a record needle, to measure its properties-- to track friction on surfaces made of diamond and silicon crystal. Each material was coated with an adsorbate, or thin surface layer, of either hydrogen atoms or deuterium, which is a hydrogen atom with an extra neutron in its nucleus.
They found that the tip sliding over the deuterium lost less energy lost as heat, apparently due to the lower natural vibration frequency of these atoms. Essentially, atoms of the probe collided with those heavier atoms less often, and losing less kinetic energy as a result, the team writes.
The findings may be interesting to industrial engineers seeking to reduce heat generation and wear in their machinery, the researchers said – or alternately, to those seeking to increase friction without increasing wear, as in automobile clutches.
However, much more work needs to be done to understand the exact mechanism of these atomic vibrations, the researchers said. The study appears in the November issue of Science.
"Heftier" Atoms Reduce Friction at the Nanoscale, Study Led By Penn Researcher Reveals [UPenn]
(Image Credit: Timsnell, via Flickr)
