2023-10-07 13:57:00
It is an everyday phenomenon that is still not fully understood: friction. A research team with participation from Regensburg has now investigated at the atomic level how heat is generated.
Making a fire with two pieces of wood, braking hard in a car or rubbing your hands in the cold season – all of these are rubbing processes that also generate heat. This phenomenon has been known to humanity since its beginnings and science has been dealing with it for a long time, with Leonardo da Vinci already investigating the so-called coefficient of friction. However, not all mysteries have been solved yet, for example when it comes to the exact contact conditions between objects.
An international research team, which included the University of Regensburg, the University of Kanazawa (Japan) and the Donostia International Physics Center (Spain), has now shed some light on the matter. Advances in scanning probe microscopy also helped.
Specifically, the research focused on dynamic friction, i.e. the force required to maintain the movement of a molecule. In contrast to static friction, in which a single molecule moves on a surface, this has hardly been researched theoretically.
Classical mechanics are not sufficient to explain this
The team led by Franz J. Giessibl from the Regensburg Chair for Quantum Nanoscience investigated how carbon monoxide molecules behave on a so-called single-crystalline copper surface – i.e. a surface with a uniform, homogeneous crystal lattice. The analysis was carried out using a special atomic force microscope, which can study atomic forces using a nanoscopically fine needle.
On the one hand, the experts checked how the carbon monoxide molecule is positioned relative to the microscope tip and the surface. To do this, they analyzed the relationship between the movement of the molecule triggered by the tip, the heat generation and the static and sliding friction.
The result: A mysterious bridge state is formed when friction occurs, which can only be described by quantum mechanics, says Giessibl. Attempts to explain things using simpler and much older classical mechanics were no longer sufficient in this case.
Forces act like an egg in an egg carton
“Friction can ultimately be traced back to the forces of atomic contact between two rubbing bodies,” explains the expert. He also gives the vivid picture of eggs in an egg carton, the depressions of which represent the preferred places of an atom “rubbing” on them. “The forces that act between atoms are not as simple in nature as the forces that an egg in an egg carton is subject to. Rather, the nature of these forces is subject to quantum mechanics,” emphasizes Giessibl.
Further research needs to be done here. However, the current investigation at least paves the way for future studies on the atomic processes involved in converting mechanical energy into heat.
The Study”Dynamic Friction Unraveled by Observing an Unexpected Intermediate State in Controlled Molecular Manipulation“is in the trade magazine”Physical Review Letters” appeared.
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