Using a mere 500 µL of lubricant, the SPM-8100FM high-resolution scanning probe microscope can analyze metallic surfaces in contact with a lubricant, at molecular level resolution. This holds promise as a new method, which will enable accelerated lubricant development by replacing a screening at the initial development stages with laboratory-scale materials testing.

LM11949 Bearingseal

When a scanning probe microscope is used, structure at the molecular level can be evaluated by acquiring a topographic image (XY) of the adsorption film originating from the additive in the lubricant, and a Z-X cross-sectional Δf mapping image.

LM11910Bearing

Engine lubricants play an important role in lubrication, cooling, cleaning, and rust prevention for vehicles, construction machinery, ships, airplanes, and other equipment with internal combustion or turbine engines. Lubricants deteriorate due to decomposition and chemical changes of oil components and additives caused by physical and thermal stresses, as well as contamination by metal wear particles and incorporated fuel. As the lubricant deteriorates through use, its performance will decline and the inside of the engine can wear, leading to a decrease in service life and potential malfunction. Therefore, it is recommended to analyze the lubricant throughout its lifespan to assess its quality, utility, and remaining service life. These analyses can be accomplished with a number of instruments.

In engine oil and other lubricants, additives are added to the base oil to improve performance. The additives form a thin adsorption film (tribofilm) on the metal surfaces of the sliding parts, reducing friction and wear. However, it is difficult to analyze the film in the lubricant. As a result, lubricant development sites repeatedly perform actual vehicle tests, engine tests, and other tests, to narrow down the search for additives and their optimal concentrations. This causes issues with time and expense.

The surface is not covered by the phosphate ester adsorption film, so the contours of the particles are clearly visible.

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Lm11949 bearingcross reference

In this example, the SPM-8100FM next-generation scanning probe microscope, which features frequency modulation, is used to analyze the adsorption structure of a phosphate ester in a base oil of polyalphaolefin (PAO) on an iron oxide substrate. It is observed that the adsorption layer is different depending on the presence or absence of the phosphate ester.

A multilayer structure is formed when the PAO molecules, which are in contact with the iron oxide film surface, lie horizontally and adopt a parallel orientation.

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The disappearance of the layered structure suggests that the PAO molecules do not make direct contact with the iron oxide film surface. In other words, the iron oxide film surface is covered by the phosphate ester adsorption film.

〔Source: Tribology No. 64, Vol. 11 (2019), Shiho MORIGUCHI, Ryohei KOKAWA, Teppei TSUJIMOTO, Akira SASAHARA and Hiroshi ONISHI: Analysis of Solid-Liquid Interface by Frequency Modulation Atomic Force Microscopy〕