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The film-forming, friction, and antiwear properties of zinc dialkylphosphates (ZDPs) were investigated and compared with the corresponding zinc dialkyldithiophosphates (ZDDPs). The primary ZDPs generally show similar friction and antiwear performance to the primary ZDDPs, although some differences are seen between them in film-forming properties. For the secondary ZDP and ZDDP, there are some clear differences in their tribological properties. This indicates that the properties of the primary ZDPs and ZDDPs may be controlled predominantly by adsorbed films consisting the intact additives and/or their decomposition compounds, and that the properties of the secondary ones may be controlled by glassy reaction films consisting zinc/iron polyphosphates.

Fuel economy has become the dominant criterion in the design of new automobiles. The globally enacted targets for fleet average emissions pose true challenges to automobile manufacturers. Increasing fuel economy requires enhancements both in hardware as well as in lubricant performance. As a key component of the lubricant, poly(alkyl methacrylate) PAMA viscosity index improvers have been identified as crucial design element due to their multiple modes of action. In their original application, they serve the well-known mechanism of polymer coil expansion at high temperatures and collapse at low temperatures. They help to flatten the viscosity/temperature relationship of the lubricant and allow for reduced low temperature viscosities and reduced internal friction, which directly translates into fuel economy. In addition to this bulk application, interfacial tribological phenomena contribute significantly to efficiency and fuel economy.

Recent work by the authors has indicated that some types of viscosity index improver polymers can form thick boundary films in lubricated contacts. These films appear to result from the adsorption of molecules of polymer on metal surfaces to produce layers, about 20 nm thick, having higher polymer concentration and thus higher viscosity than the bulk solution. In the current paper it is shown that these VII boundary films are able to separate rubbing surfaces in both rolling and sliding contacts and that they make a significant contribution towards reducing friction and wear at temperatures up to at least 140°C. The mechanism by which these polymers reduce friction and wear is elucidated.

Polyalkylmethacrylates (PAMAs) are widely used as viscosity index improvers and dispersant boosters in engine, transmission and hydraulic oils. They have been shown to be able to adsorb from oil solution on to metal surfaces, to produce thick, viscous boundary films. These films enhance lubricant film formation in slow speed and high temperature conditions and thus produce a significant reduction of friction and wear. In a recent systematic study a range of dispersant and non-dispersant PAMAs has been synthesized. The influence of different functionalities, molecular weights and architectures on both boundary film formation and friction has been explored using optical interferometry and friction-speed charting. From the results, guidelines have been developed for designing PAMAs having optimal boundary lubricating properties. In the current paper the film forming, friction and wear properties of solutions of two functionalised PAMAs is first described.