Nanoscale Investigation of the Surface Reactivity of Ionic Liquids under Harsh Tribological Conditions

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.

The impact in the short (i.e., during the project), medium (i.e., within 5 years from the end of the project), and long (i.e., >10 years from the end of the project) term of the project can be divided into three main themes: a) knowledge; b) economic; and c) society.
a. Knowledge impact. i) In the short term, I will investigate the promising lubricating properties of a class of ionic liquids (ILs) through the use of a novel methodological approach based on advanced surface-analytical techniques with exceptional sensitivity and spatial resolution. Additionally, I will innovatively use national synchrotron facilities to study the surface reactivity of ILs. Researchers at the University of Leeds and other research-intensive institutions (both academic and industrial) can benefit from these methodological developments to tackle unanswered questions of significant technological relevance in other fields, such as corrosion and wear evaluation of coatings (e.g., silicon nitride) that can potentially increase the longevity of prosthetic hip joints; ii) in the medium term, the development of an understanding of the relationship between chemical composition and tribological performance for ILs will provide guidance for designing ILs able to meet the performance requirements of advanced applications. Chemists in R&D in the automotive (e.g., Total, BP, Lubrizol) and microelectronics (e.g., HGST) sectors will be the beneficiaries of such knowledge: the synthesis of ILs that can provide the functional behaviour required for specific applications (e.g., engine oils, lubricants for hard disks) will not rely on a trial-and-error approach, but on a rational design based on the selection of chemical functionalities needed to achieve the desired performance; iii) in the long term, the availability of energy-efficient, environmentally-compatible ILs with improved tribological performance will benefit a number of industries, including those in the automotive sector (e.g., Total, BP, Lubrizol). In particular, the use of ILs in engine oil formulations will help meeting future fuel efficiency requirements and decreasing the environmental impact of passenger cars. The exploitation of current state-of-the-art technology for friction reduction in automobiles has been estimated to potentially reduce friction losses in cars by 61%, which could translate in an enormous economic saving and a reduction of carbon dioxide emissions. The employment of ILs by the automotive industry will contribute to further reduce frictional losses and greenhouse gas emissions.
b. Economic impact. i) In the short term, the strategies for synthesizing novel ILs with task-specific performance developed during the project can lead to filing patents concerning the newly synthesised chemistries, while exploring, in the medium term, possibilities to develop commercial opportunities at the University of Leeds (including starting a spin-off); ii) in the long term, the study will contribute to the UK economy through the commercialization of knowledge (to wind turbine, aerospace, microelectronics and automotive companies, such as Total, BP) necessary for the synthesis of ILs with tailored properties for specific applications, thus providing tax revenue, adding to the UK economy, and generating wealth in the UK.
c. Society impact. The employment of ILs as lubricants for engines and turbines can enhance sustainable development through the reduction of the economic (e.g., reduced fuel expenditure) and environmental (e.g., less pollution) impact of tribology, while being a key factor in the attempt of achieving the challenging environmental objective of reducing the greenhouse gas emission (as per the 2015 UN Climate Change Convention). Notably, the rational synthesis of improved ILs can play a crucial role in attempting to achieve the fuel efficiency target set by European environment and transport ministers for 2025, i.e., 95 g of CO2 per km (average value in 2014: 123 g CO2 per km).