There was explored a new type of fundamental friction forces acting on the nanoscale


Looking for components for nanomachines and nanosystems, which create in its motion very small friction, scientists from the Munich University of Technology (TUM) headed by professors Thorsten Hugel and Alexander Holleitner  investigated the behavior of polymer molecules, dissolved in a solvent, which are attracted to the surfaces of certain materials.

The aim of this research was to study the action of the basic laws of physics at the molecular level in order to use the gained knowledge in the development of anti-friction surfaces and new types of lubricants. In the course of these studies, scientists unexpectedly found another type of friction forces, which occurs on the nanoscale level.

Making their research, the scientists put an end of the polymer molecule on the tip of an atomic force microscope (AFM). The second end of the molecule along with the tip of the microscope moved along the test surface of particular material. This combination allowed using AFM-microscope to measure the value of the frictional forces experienced by the polymer molecule during movement on the surface.
In addition to the two known mechanisms of friction forces, such as gravity and sliding, the researchers found a third mechanism, which appears only at the certain combinations of polymeric material, surface material and solvent. The researchers called this mechanism "desorption stick".

"Despite the fact that molecule of the polymer during its movement is pressed to the surface, one edge of the molecule could begin stretching into the surrounding solution without any visible effect by known forces, thereby creating an additional resistance, i.e. friction" - said professor Hugel - "Most likely, the reason is in low internal friction within the polymer molecule."

According to the existing information, the new friction mechanism does not depend on the speed of movement, the pressing force and the surface adhesion properties of the polymeric material. It depends on the chemical properties of the surface material and the type of solvent used. For example, the hydrophobic surface of the foam demonstrates a complete lack of the third friction mechanism when the polymeric material is dissolved in chloroform , the material , when dissolved in water, the third force of friction (desorption stick) appears strongly enough.

"Understanding the processes, which lead to the appearance of friction forces, studied by us with one single molecule , open up entirely new ways to minimize friction " - says Professor Holleitner - "In the future, a special preparation of polymeric materials suitable for different kinds of surfaces , will allow to create nodes and mechanisms, which are not exposed or weakly exposed to friction and not only on the nano and micro levels. The same methods can be successfully applied at the conventional level , reducing the friction and wearout of parts and components of various mechanisms, including automobile engines. "

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