Page 29 - Shimadzu Journal vol.8 Issue2

Hydrocarbon Processing Industry

Applications of

Frequency-Modulation Atomic Force

Microscopes (FM-AFM) to Lubricant

Hideo Nakajima, Product Manager (Microscope), X-ray/Surface Business Unit
and Global Application Development Center, Analytical & Measuring Instruments Division, Shimadzu Corporation

Tribology (technology related to lubrication, friction, and wear) unthinkable. In this context, frequency-modulation atomic force
is fundamental for a wide variety of mechanical instruments and microscopes (FM-AFM) can capture the shape (XY) of solid sur-
related markets are widespread. Lubricant improvements and re- faces in liquids and cross sectional images (Z-X) of solid-liquid in-
search into the material properties of solid surfaces are convention- terfaces with high resolution. These instruments have become a
ally performed experientially. However, there is a pressing need focus of attention as a new method for clarifying the structure of
to systematically assess lubrication interfaces through microscopic lubricant at solid-liquid interfaces at the molecular level (Fig. 1).
observations, based on the ever growing interest in reducing loss FM-AFM is commercially available from Shimadzu as the
and saving energy. SPM-8100FM model. Here, we will briefly describe two examples
For example, with automotive oil, the need for reduced fuel of applications of this instrument to lubricant.
consumption in environmentally friendly automobiles is accelerat- (1) In this example, an adsorption film of a phosphate ester
ing the reduction of base oil viscosity, with an aim to reduce resist- (C18AP) added to a base oil (Poly-α-Olefine: PAO) as an anti
ance to stirring. At the same time however, the oil film on sliding friction agent was analyzed with respect to its formation on
parts becomes thinner as the viscosity of the base oil is reduced, an iron oxide surface. At the lubricant-iron oxide interface,
which leads to concerns about reductions in seizure and wear re- when PAO on its own was applied, a layered structure was
sistance. Many cases have been reported of improvements from observed due to the orientation of the PAO molecules. Next,
additives used as countermeasures. Though additives are known to when C18AP was added to PAO, it was found that as the
form an adsorption layer on metal surface, it is difficult to analyze concentration of C18AP was increased, the layered structure
this adsorption layer with high resolution within lubricant. As a disappeared. The disappearance of the layered structure im-
result, many uncertainties remain regarding this formation process plied that the C18AP adsorption film was coating the iron
and the mechanism of its action. oxide surface and was disrupting the orientation of the PAO
In recent years, due to advances in analytical techniques, anal- molecules. Macroscopic wear tests were performed on a sim-
yses have become possible that would have been conventionally ilar lubricant and a correlation was obtained between the

Shimadzu Journal vol.8 Issue2 71