A review of recent advances of ionic liquids as lubricants for tribological and thermal applications

Abstract

The novel characteristics of ionic liquids (ILs) led to an improved tribological and thermal performance. This article discusses current progress in developing ILs as neat lubricants or additives in lube oils, with a focus on ILs chemistry, synthesis, miscibility, and other relevant rheological, thermal, and tribological properties at macro to nanoscales. This article also introduces a review of lubrication mechanisms based on the tribofilm formed on the rubbing interfaces owing to tribochemical reactions among the ILs, base oil, and solid bodies, which shows key insights into anti-wear properties. ILs exhibited superior anti-wear properties compared to fully formulated oils. Notably, there was no symmetry between the friction results of ILs and their wear counterpart. Furthermore, the main challenges to further improve ILs performance for tribological applications are highlighted. Eventually, prospects for ILs tribology are suggested, which will guide the development and synthesis of ILs-based lubricants for tribological applications.

Experimental Investigation of Tribological and Rheological Behaviour of Hybrid Nanolubricants for Applications in Internal Combustion Engines

“…ILs are molten salts at room temperature that possess unique physicochemical properties and have shown good oil-soluble and excellent lubricating properties, especially protic ILs with long alkyl chains [23][24][25][26]. Among the myriad of existing protic ILs, phosphonium cation-based ILs exhibit outstanding solubility in non-polar liquids, thus facilitating their use as ILs in conventional lube oils [27]. Since the International Lubricants Standardization and Approval Committee specification (ILSAC GF-5) restricts the phosphorus content to a range of 0.06-0.08 wt% [28], considering the molecular weight of phosphonium ILs, previous work has used a concentration of 1 wt% of these ILs in engine lubricants [24,28,29].…”