Abstract
Oleamide and Synovene lubricant additives when mixed together show a clear co-operative effect leading to friction and wear reduction. Sum Frequency Generation vibrational spectroscopy has been used to record in situ spectra of these additives with the aim of understanding the behaviour of these molecules when adsorbed on steel immersed in a model base oil at pre-selected temperatures. The spectra of the individual components and of mixtures have been recorded up to 130 °C. Individual spectra from both molecules have been distinguished using per-deuterated oleamide. The temperature at which maximum ordered adsorption of pure Synovene molecules occurs drops from ~ 130 to ~ 70 °C in the mixture with oleamide. Our results show that co-adsorption occurs, which causes a change in net polar orientation of the oleamide component suggesting the hydrocarbon chains of the oleamide molecules reverse their polar orientation when Synovene is present. The net effect of co-adsorption and change in orientation as well as conformation of the two molecules could explain the reduction of friction and wear observed at the metal–metal interface.
Highlights
Small amounts of friction modifiers and anti-wear additives added to lubricating oil play a vital role in improving friction and wear performance in tribological contacts, resulting in reduced fuel consumption and lower carbon emission both of which are desirable environmental goals [1, 2]
In combination there is an additional decrease in the coefficient of friction (CoF) indicating a co-operative effect of the additive mix within the initial 20 min rubbing contact suggesting that the mode of action of the additives in the model system is consistent with that observed in the engine tests of fully formulated oils
Sum Frequency Generation (SFG) vibrational spectroscopy has been used to gain insight into the friction and wear reduction mechanisms of two lubricant additives Synovene and oleamide at a molecular level. When these two additives adsorb on steel from a model base oil at temperatures up to 130 °C, at least some parts of their hydrocarbon chains orientate perpendicular to the surface
Summary
Small amounts of friction modifiers and anti-wear additives added to lubricating oil play a vital role in improving friction and wear performance in tribological contacts, resulting in reduced fuel consumption and lower carbon emission both of which are desirable environmental goals [1, 2]. The application of analytical surface science techniques in determining the structure of the protective layers formed by such additives in model lubricants (additive and additive combinations in base oil) under thermal and tribological conditions is important for gaining a better understanding of lubricant performance [3, 4]. Changes in the adsorption of Synovene and oleamide onto steel on their own and from mixtures in base oil as a function of increasing temperature are investigated by SFG to monitor the structural behaviour of their aliphatic chains
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