Title:	Orthoborate-based ionic liquids interaction with solid surfaces - a first principles study
DNr:	SNIC 2020/5-118
Project Type:	SNIC Medium Compute
Principal Investigator:	Oleg Antzutkin <olan@ltu.se>
Affiliation:	Luleå tekniska universitet
Duration:	2020-02-28 – 2021-03-01
Classification:	10403
Homepage:	https://www.ltu.se/staff/o/olan-1.11591
Keywords:

Abstract

The physicochemical properties of ionic liquids have been intensively studied over the past two decades, because of their unique properties making them candidates for a range of applications, one of which is tribology. Our experimental work on ionic liquids as lubricants and additives to lubricants leads to interpretations and hypotheses that can only be validated by accurate first-principles simulations based on quantum mechanical methods. One such hypothesis is how surface restructuring due to the lubrication and formation of tribofilms affects the tribological characteristics of the contact pair lubricated by an ionic liquid or an oil blend with ionic liquids as additives. We have observed experimentally a significant decrease in both friction and wear for a range of orthoborate-based ionic liquids designed in our research groups. We have also found that some of our orthoborate-based ionic liquids have a limited stability at surfaces of different metal oxides (MgO, Al2O3 and SiO2), particularly, at elevated temperatures, i.e. at >110 °C. While, some other orthoborate-based ILs are stable at these surfaces up to 200 °C. A few hypotheses were put forward to explain these phenomena, one of which involves proton transfer in the structure of orthoborate anions at silica surfaces catalysed by Si-OH groups. Using density functional theory (DFT) simulations, we would like to test how different orthoborate-based ILs interact with the underlying silica substrate. Unravelling of the ionic liquid interaction with different solid surfaces is crucial for understanding of both friction and wear and it can be a useful tool for future design of novel classes of ionic liquids for a variety of technical applications. Since the boundary film of ILs at lubricated surfaces is self-healing we can design ILs with a high potential for the lubrication market. However, excessively reactive lubricants could also cause tribochemical corrosion of the surfaces and shortened machine life. Thus, there is a narrow balance between IL stability and reactivity of the ionic liquid at the interfaces in the IL-lubricated contact. The actual binding of the IL ionic components to silica, MgO and Al2O3 substrates has been studied by us experimentally, and has indicated plausible interactions resulting in observed isomerisation of the anionic ligand of one of the selected IL, namely, [P6,6,6,14][BMB], that can only be verified through DFT simulations. We also plan to investigate other substrates.