Researchers at research institute MESA+ of the University of Twente and Forschungszentrum Jülich have proven that the friction between two surfaces can be greatly reduced by using artificial ‘polymer brushes’. They have developed a new process whereby the 'polymer brushes' on a surface attract an extremely fluid lubricant and keep it in place. The method was inspired by nature, based on the extremely low friction found in joints. The research was published in the authoritative scientific journal Nature Communications.
Lubrication is needed wherever moving parts come into contact with one another. It prevents fixed parts from touching one another and ensures optimum working between cogs, ball bearings and valves. An ideal lubricant has to fulfil seemingly incompatible requirements: it has to be as thin as possible – in order to reduce friction – but thick enough to remain in the area of contact. In practice, fats and oils are usually deployed.
Conversely, biological lubrication such as that in joints, works much more efficiently. Polymers stick out on the cartilage at the end of our bones and form 'brushes' which ensure that an incredibly fluid lubricant is attracted and kept in place. During recent decades many researchers have tried to imitate this natural model technically, but with little success because the tentacle-like polymers on the surfaces facing one another have a tendency to become entangled.
Two polymers, two lubricants
In a study published in the scientific journal Nature Communications, researchers from research institute MESA+ of the University of Twente and Forschungszentrum Jülich have shown that the solution is to use two different polymers and two lubricants. A water-soluble polymer on one surface and a water-repelling polymer on the other, and one water-based solvent and one oil-based solvent.
90 times less friction
One of the researchers involved is Dr. Sissi de Beer, who used to work for Jülich and is currently affiliated with the department of Materials Science and Technology of Polymers of the University of Twente. She carried out the first part of the study while with Jülich, where, together with colleagues, she used a supercomputer to carry out simulations. These simulations showed that the polymers did not become entangled with one another. Together with colleagues at the University of Twente, and using an atomic force microscope, she subsequently managed to provide the experimental evidence. It turned out that in comparison with a system with a single type of polymer, friction was reduced by a factor of 90.
De Beer explains how it works: “The two different fluid phases split up because they repel one another. This keeps the polymers in their place and at the same time prevents them from becoming entangled with the other brush via the interface.”
Illustration credits: Nolux Media
The two-component lubricant is interesting for a lot of applications. For example, a simple pump system, such as a syringe, which would be able to administer the tiniest quantity of medicine with extreme accuracy. In particular the new process could provide minimal friction solutions in situations involving high local pressure and enormous forces, for example, in axle bearings and hinges. An alternative still has to be found for the most commonly used lubricant – engine oil – because polymer brushes cannot withstand high temperatures.
Dr. Sissi de Beer