Motor oil mysteries =================== At MU's research reactor, a band of scientists uses neutron beams to probe [motor oil mysteries] ------------------------------------------------------- By Uwe Muench Special to the Missourian ------------------------- The reasons chemicals within motor oil lubricate a car's engine remain a mystery, which MU scientists hope to unravel. MU physics professor Haskell Taub and his research group use neutron scattering at the MU Research Reactor to understand lubrication's underlying secrets. Their painstaking work may improve motor vehicles and their performance in the future. Ideally, Taub's current basic research, if someday applied, could "reduce the amount of friction between the various moving parts ... And this can make the engines more efficient, use less gasoline, increase the life of an engine." Taub says. While motor oil keeps cars and trucks running, oil manufacturers have never understood why. What the oil companies are doing in their research is mainly trial and error, Dirk Fuhrmann, a German scientist in Taub's group, explains. "Our work is totally different," he said. Taub and his students use neutron beams to see how oil molecules stick on a solid surface, if and how they build an ordered structure, and how oil's atoms move along the surface. "If you know this molecule is better than the other one, we can make decisions which kind of molecule we have to choose for good lubricants." Fuhrmann says. Motor oil is a mixture of many kinds of different chemicals called alkanes. Alkane molecules "contain a backbone of carbon atoms in a zigzag shape," Taub says. They are "flexible, chainlike molecules,... that are not rigid, but can bend and twist." In the lab, in their pure form, alkanes look "like paraffin, so it looks like candle wax at room temperature." In the late 60's oil companies such as British Petroleum performed experiments to find out whether alkanes connect to surfaces with their skeletal structures parallel to the surface or if they look like worms standing on end. Indirect conclusions showed the alkanes lie down. It remained unclear up to the late 1980s whether alkanes' molecules arrange themselves in a regular pattern. Once scientists detect a molecule's arrangement on a surface, they are better able to understand how it works and if its performance might be improved. When even the Nobel Prize-winning technique of Scanning Tunneling Microscopy could not completely resolve the structure of alkanes, Taub realized he should try to build on his experience with neutron scattering to gain some insight. In elastic neutron scattering or diffraction, the neutrons of the MU Research Reactor are thrown like balls at the alkane monolayer and the different angles the neutrons reflect at show the spacing between the molecules on the surface. The spacing helps determine the molecule's shape, orientation and structure pattern on the surface. Taub is currently investigating some alkanes that have branches. "In addition to the carbon backbone, there are side-chains along the length of the alkane; and for reasons that people really don't understand at the microscopic level, these branched alkanes have better lubricating properties than the normal ones," Taub says. Taub compares the structures of both branched and normal alkanes. "We can maybe determine what is it about the branched alkane that makes it the better lubricant." The reactor experiments are conducted "not on a metal surface like it would be in a car engine, but on a more ideal surface that we can characterize very well, and know it's free of defects," Taub explains. Defects disturb the molecules, and removing them decreases the possibility of investigator errors. Graphite, which is commonly used in pencils, is an ideal surface for Taub's experiments because of its large surface area. Leah Criswell, one of the MU doctoral students in Taub's group, holds a 1.5-by-2-inch graphite sample. "If you see a sample of this size and you think it has a surface area of a football field, that's mind-boggling." That is because graphite is layered in extremely thin slices. It takes two weeks to prepare a graphite sample for scrutiny at the reactor. Graphite is baked in a vacuum to get rid of impurities. Then it is frozen with liquid nitrogen, and the exact surface area is determined. After a first measurement at the reactor, alkane molecules are added inside a glove bag, separating the sample from the atmosphere. "Don't forget to take off your diamond wedding ring," Criswell quips. The alkane sample is baked twice in addition to other procedures, so it is vaporized and distributes equally on the graphite surface. Finally, the reactor provides neutrons to shoot at the sample. Recently Taub's group also started investigating how normal and branched alkanes move along the surface. The molecules "can be flexible, they can stretch, and in addition the whole molecule may move across the surface..., just like an ink droplet would diffuse in a glass of water," Taub explains. Fuhrmann predicts the branched alkanes will move more slowly. He believes they are stiffer because of their branches. Some of the Taub team's experiments to measure the alkanes' speeds occur at the National Institute of Standards and Technology near Washington and at the Argonne National Laboratory near Chicago. MU's research reactor still performs preliminary experiments on the graphite samples as preparation even for these internationally famous reactor sites, Fuhrmann explains. Taub notes that his work with the alkanes within lubricants illustrates how basic research in physics assists both scientific understanding and has real-world potential applications. "Physicists are fond of finding the simplest possible physical system that exhibits a particular problem," he said. --------- Uwe Muench is a physicist working at MU on his doctoral degree.