Fundamentals of organic friction modifier behaviour

Abstract

Organic friction modifiers have long been added to oil formulations to help improve lubricity, particularly in the boundary lubrication regime. Many aspects of organic friction modifier behaviour remain unknown. In this thesis these aspects are isolated and probed using numerous different techniques. Organic friction modifiers are amphiphilic molecules comprising a head group and a hydrocarbon chain. The chemistry of the organic friction modifier employed affects the observed film forming properties and frictional behaviour. Factors of interest include the effects of the head group type and of alkyl chain unsaturation. Commercially employed organic friction modifiers tend to comprise a mono-unsaturated oleyl group. This project deals with the impact this has on organic friction modifier performance. Another area of interest is the behaviour of glycerol monooleate. Glycerol monooleate is one of the most commercially employed organic friction modifiers and is atypical to model organic friction modifiers in that it has a rather bulky polar moiety. Model organic friction modifiers usually have only one functional group; however, glycerol monooleate has two alcohol groups and an ester group. Although glycerol monooleate is widely employed in oil formulations, many aspects of its behaviour remain uncertain. In this thesis several techniques are used including upscale friction experiments such as High Frequency Reciprocating Rig tests, Ball on Disc pure sliding friction tests and Mini-Traction Machine mixed sliding-rolling tests. Organic friction modifier film formation on ferrous and non-ferrous surfaces is investigated in situ from solution in hydrocarbon solvent using the Atomic Force Microscope. Organic friction modifier films formed on surfaces during friction tests are investigated ex situ by Atomic Force Microscopy and Time-of-Flight Secondary Ion Mass Spectroscopy.