Reduction of Friction by Functionalised Viscosity Index Improvers |
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Authors: | J Fan M Müller T Stöhr H A Spikes |
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Affiliation: | (1) Tribology Group, Department of Mechanical Engineering, Imperial College London, London, UK;(2) RohMax Additives GmbH, Darmstadt, Germany |
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Abstract: | A range of functionalised polymethacrylate copolymers have been synthesised with different functionalities, polymer architecture
and molecular weight. It is shown that appropriately functionalised block copolymers give enhanced film thickness and greatly
reduced friction under low entrainment speed conditions, even with polymer concentration as low as 1% wt. This behaviour almost
certainly results from the formation of an adsorbed brush-like film of thickness ca 20 nm on each polar surface. These films provide a highly viscous inlet that promotes fluid entrainment and thus maintains
a separating film down to very low entrainment speed. The adsorbed polymer films are also able to maintain separation in stationary
contact conditions. Randomly distributed copolymers do not show this type of behaviour. The friction reduction observed is
more effective in unidirectional, mixed sliding–rolling than in reciprocating, sliding conditions. However, it is found that
functionalised polymers and conventional organic and molybdenum-based friction modifiers can be combined to provide effective
friction reduction over the whole range of rubbing conditions. |
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Keywords: | Elastohydrodynamic lubrication Mixed lubrication Boundary lubrication Additive Viscosity index improver Polymethacrylate Functionalised polymer Friction MoDTC |
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