Hiroko Ohtani

Modification of Boundary Lubrication by Oil-Soluble Friction Modifier Additives

The molecular-level function of model and commercial friction modifier additives in lubricants of the type used at the wet clutch interface in automatic transmissions has been studied using a surface forces apparatus (SFA) modified for oscillatory shear. The nanorheological properties of tetradecane with and without a model friction modifier additive (1-hexadecylamine) were examined in the boundary lubrication regime and compared to a fully-formulated automatic transmission fluid (ATF). 1-Hexadecylamine adsorbed as a single layer on the sliding surfaces, reduced the static frictional force and the limiting shear stress, and eliminated the stick–slip transition that exists in pure tetradecane. The ATF, which contains commercial-grade friction modifiers, showed nanorheological properties similar to those observed for tetradecane containing 0.1–0.2 wt% 1-hexadecylamine.

Molecular dynamics simulation study of model friction modifier additives confined between two surfaces

We have used molecular dynamics simulations to investigate the molecular energetics and orientation of surfactant‐like model “friction modifier” (FM) additives with and without hydrocarbon solvent and confined between idealized atomistic surfaces. The normal load, fluid layer thickness, and additive surface concentration dependencies agree favorably with those measured experimentally for model fluids using a surface forces apparatus. The simulations predicted either a single or multiple free energy wells with increasing surface separation, depending on the FM concentration. With no solvent added, pure FMs showed oscillations in normal pressure and free energy with increasing surface separation; stable states corresponded to successive layers of FM molecules being expelled from the region between the adsorbed films. In the case of FM/hydrocarbon solution, only a single stable position was found. The equilibrium structure was also found to depend on the head group structure of the FMs.

New opportunities in automotive tribology

In this article we give an introduction to the field of automotive tribology as a guide to the following articles in this focus issue, and we review the recent application to automotive tribology of several molecular and microscopic level techniques. These include scanning force microscopy (SFM), nanohardness techniques, surface forces apparatus (SFA), computer modeling, vibrational spectroscopies, three UHV‐surface science techniques, and microcalorimetry. They are currently being used, in conjunction with more traditional techniques, to further both practical and fundamental knowledge of automotive tribological systems.