A Review of Ionic Liquids for Green Molecular Lubrication in Nanotechnology

Abstract

Common industrial lubricants include natural and synthetic hydrocarbons and perfluoropolyethers (PFPEs), where the latter is widely used in commercial applications requiring extreme operating conditions due to their high temperature stability and extremely low vapor pressure. However, PFPEs exhibit low electrical conductivity, making them undesirable in some nanotechnology applications. Ionic liquids (ILs) have been explored as lubricants for various device applications due to their excellent electrical conductivity as well as good thermal conductivity, where the latter allows frictional heating dissipation. Since they do not emit volatile organic compounds, they are regarded as ''green'' lubricants. In this article, we review the different types of ILs and their physical properties responsible for lubrication. We also discuss their suitability as lubricants, since the long-term performance of ILs as lubricants may be affected by issues such as corrosion, oxidation, tribochemical reactions, and toxicity. We present nanotribological, electrical, and spectroscopic studies of IL films along with conventional tribological investigations, recognizing that understanding the tribological performance at various length scales is a crucial step in selecting and designing effective lubricants.

Ionic liquids as an additive in fully formulated wind turbine gearbox oils

“…Different FAP-anion based ILs have been studied both as additive and as a neat lubricant for different materials pairs exhibiting excellent friction and wear reducer behaviour [20][21][22][23][24][25][26]. Some review papers [29][30][31][32] have detailed the advantages of using ILs in tribology, their thermal and oxidative stability, and their tribochemical reactions.…”

Isoconversional kinetic analysis applied to five phosphonium cation-based ionic liquids

“…A lot of researches have been published concerning the use of ionic liquids as lubricants since 2001 [29], proving their remarkable potential for this purpose [4,6,[30][31][32]. At the beginning, imidazolium-based ionic liquids with [PF 6 ] and [BF 4 ] anions were widely used [33][34][35].…”

Self-lubricating, wear resistant protic ionic liquid-epoxy resin

“…Room-temperature ionic liquids (ILs) [11,12] contain bulk organic cations and organic or inorganic anions and show a unique combination of properties such as their low volatility, non-flammability, and their high thermal stability which are most relevant for tribological applications. ILs have shown excellent tribological performance, not only in lubrication of metal alloys and ceramic materials under severe sliding conditions [13][14][15][16][17][18][19][20][21][22][23][24][25], but also in the very difficult task of achieving the reduction of friction coefficients and wear rates of thermoplastic polymers and epoxy resins, where they have been used both as external lubricants and as additives [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. Ionic liquids are also making an increasing impact in the field of polymer science, in particular on the development of new epoxy networks and composite materials by acting as curing agents, plasticizers, and as dispersants of nanophases in the epoxy matrix [35][36][37][38][39].…”