Super-slippery surfaces developed by Swedish researchers

Wednesday, April 2, 2008

How to decrease friction between surfaces? Researchers at KTH, Stockholm University and the Institute for Surface Chemistry (YKI) have been able to reduce friction and produce super slippery surfaces by selecting material based on the van der Waals forces.

In a cooperative effort between the researchers Mark Rutland (KTH), Lennart Bergström, (Stockholm University) and Adam Feiler (YKI) it has been possible to demonstrate for the first time that the friction between two surfaces that are exposed to the van der Waals repulsion force is very close to zero. Results have been published in the Langmuir scientific journal.

Van der Waals forces usually attract, which results in adhesion, i.e. the molecular attraction that exists between two bodies in close contact achieves a considerable level between individual molecules and between surfaces. However in a few systems (when two surfaces are in close contact with a liquid between them) this attraction can be transformed into repulsion which increases in strength the closer the surfaces come to each other. These surfaces are then more attracted to the liquid than they are to each other, and consequently do not wish to come into contact with each other if they are immersed in the liquid.

“The unique thing with van der Waals repulsion forces is that they prevent contact between surfaces, even when the surfaces are pressed together,” says Professor Lennart Bergström, Stockholm University.

By utilizing the van der Waals repulsion forces when selecting material, the researchers have been able to eliminate adhesion and drastically reduce friction, thus producing super-slippery surfaces.

“For example our results show that the friction between a particle of gold and a Teflon surface immersed in cyclohexane is actually so low that it is not measurable, not even with an atomic force microscope; an instrument that is routinely used to measure forces between molecules,” reports Professor Mark Rutland, Department of Surface Chemistry at KTH.

Low friction levels are extremely important if, for example, turbines in windmills, micro engines or hip joint replacements are to work well. According to researchers there are a number of material combinations that can provide super-slippery, low friction surfaces.

“For example there could be a ball bearing made of metal in a Teflon ring, or perhaps make engine components that are exposed to friction from certain combinations of ceramic material,” states Professor Mark Rutland, KTH.

Source: KTH - Royal Institute of Technology

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Time Stamp: 4/2/2008 at 11:34:32 AM CST