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Energy and resource losses in moving mechanical components as a result of friction and wear impose an enormous cost on national economies (in the UK the economic impact caused each year by friction and wear is estimated to be ~2% of the gross domestic product, i.e., £25 billion). As one particular example, one-third of the fuel used in passenger cars is employed to overcome friction in the engine, transmission, tyres, and brakes. For a single passenger car, this corresponds to approximately 340 litres of fuel per year, at a cost of £380 according to the average UK gas price in 2015, being spent in overcoming frictional losses. This results in wasted energy and unnecessary environmental emissions. The exploration of new classes of energy-efficient, environmentally-compatible lubricants, which can reduce friction and wear in engines, turbines, microelectronics, etc., is thus becoming increasingly important. In particular, it will be a key factor in attempting to achieve the challenging environmental objective of reducing greenhouse gas emission set during the 2015 UN Climate Change Convention. In the case of passenger cars, as an example, the new fuel efficiency target set by European environment and transport ministers for 2025, i.e., 95 g of CO2 per km (for comparison, the average value in 2014 was 123 g CO2 per km), constitutes a great challenge for scientists and engineers, who are now required to develop novel technical solutions and functional materials to improve car efficiency and decrease their environmental impact. The research in this study will contribute to this by providing novel insights into the physico-chemical basis underlying the promising properties of a class of "green" lubricants, namely ionic liquids (ILs), which have been recently synthesized and proposed as replacements of traditional lubricants or lubricant additives for a variety of applications, including automobile engines, microelectromechanical systems, hard disks, and aerospace. As an example, the low volatility of ILs makes them attractive as additives for engine oils, since the generation of no hazardous volatile compounds avoids blocking filters and catalyst degradation in the exhaust after-treatment systems, a concerning issue for existing lubricant additives. During the course of this research, a fundamental understanding of the mechanism of action of a class of ILs (imidazolium alkyl sulphate/phosphate) will be developed through the nanoscale investigation of their molecular reactivity on solid surfaces under mechanical contact and shear stress. To achieve this, a novel methodological approach, which is based on state-of-the-art advanced surface-analytical techniques with exceptional sensitivity and spatial resolution (including synchrotron-based techniques), will be used. The outcomes of the research, providing a starting point for rationally designing modified ILs with task-specific performance, can lead to the synthesis of energy-efficient, environmentally-friendly lubricants that are suitable for a variety of industrial applications (e.g., automotive, aerospace, microelectronics) and that can enhance sustainability through the reduction of the economic and environmental impact of tribology.
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