Many scientists, in different parts of the world, are looking for ways to reduce friction, and are trying to develop new and effective lubricants
Prof. Jacob Klein. reduce friction
Friction is one of the oldest problems humans are trying to solve and prevent. In a wall painting from 2400 BC, Egyptians are seen pouring a liquid, as a lubricant, in front of a sled-trailer used to transport a statue. Today, lubricants are needed wherever moving parts operate, in various machines, as well as in computers, airplanes and missiles. Many scientists, in different parts of the world, are looking for ways to reduce friction, and are trying to develop new and effective lubricants.
One method that has been used for more than fifty years is the boundary pin: each of the rubbing surfaces is covered with a thin layer, one molecule thick, of a lubricant. The molecules in the lubricant include "heads" that have a positive electrical charge, so they stick to the surface of the rubbing material surface, and "tails" that wiggle outwards. The surfing, or the skating
of the rubbing surfaces, takes place between the tails of the lubricant on both sides, thus reducing the friction and wear of the surfaces significantly.
Prof. Jacob Klein from the Department of Materials and Surface Research at the Weizmann Institute of Science, together with scientists from the University of Oxford in England, showed that when a system of rubbing surfaces coated with such lubricant molecules operates underwater, the friction is reduced by 99% or more. Why is friction so greatly reduced under water? Prof. Klein and his research partners investigated and found that the water molecules were attracted to the "heads" with the positive charge of the lubricant, and created a layer around them that acted as a sort of "water slide" (the rubbing surface represents the slide, the heads of the lubricant molecules represent the carpet on which the surfer sits, and the layer of water between them minimizes the friction between them). That is, when the system operates under water, the reduction in friction is not due to the reduced grip between the "tails" of the molecules of the lubricant, but from the reduction in grip between the heads of these molecules and the surface itself, as a result of the presence of water between them. In this way, a much more effective lubrication is obtained.
Another examination of the phenomenon revealed that when water is added to rubbing surfaces, the gap between the surface and the lubricant layer increases by exactly the size of a water molecule. In another experiment, in which the lubricant was replaced with a material whose molecular "heads" covered only parts of the surface, rather than the entire surface, less water entered the spaces between the "heads" and the surface, and the overall reduction in the level of friction was smaller. At this point, the scientists decided to test their theory in another way. They created a kind of "seal" that is impermeable to water, around the "tails" of the molecules of the lubricant. In this situation, they added water to the system, and tested the level of friction. The result: the level of friction was reduced to exactly the same extent as in the normal system. That is, the water really affects by reducing the friction between the "heads" of the molecules of the lubricant and the surface, and not by any effect on the properties of the "tails" of these molecules.
"These findings may lead to the development of various medical applications," says Prof. Klein. "Living organisms use lubricants, for example between joints, to prevent wear and tear of tissues, or between other living organs. It is possible that they do this through the 'boundary pin' that we described. If this is indeed the case, then the findings of this research may lead, in the future , for the development of ways to reduce friction in orthopedic implants, for new medical treatments for joint problems, as well as for a better understanding of friction processes in various biological systems."
