Effect of Ionicity of Three Protic Ionic Liquids as Neat Lubricants and Lubricant Additives to a Biolubricant

Abstract

Friction and wear of sliding surfaces are responsible for important energy losses and negative environmental effects. The use of environmentally friendly and cost-effective protic ionic liquids as neat lubricants and lubricant additives has the potential to increase the efficiency and durability of mechanical components without increasing the environmental damage. In this work, three halogen-free protic ionic liquids with increasing extent of ionicity, 2-hydroxyethylammonium 2-ethylhexanoate, 2-hydroxymethylammonium 2-ethylhexancate, and 2-hydroxydimethylammonium 2-ethylhexanoate, were synthesized and studied as neat lubricants and additives to a biodegradable oil in a steel–steel contact. The results show that the use of any protic ionic liquid as a neat lubricant or lubricant additive reduced friction and wear with respect to the biodegradable oil. The ionic liquid with the lowest ionicity reached the highest wear reduction. The one possessing the highest ionicity presented the poorest friction and wear behaviors as a neat lubricant, probably due to the more ionic nature of this liquid, which promoted tribocorrosion reactions on the steel surface. This ionic liquid performed better as an additive, showing that a small addition of this liquid in a biodegradable oil is enough to form protective layers on steel surfaces. However, it is not enough to accelerate the wear process with detrimental tribocorrosion reactions.

Influence of Hydrogen Bonding and Ionicity of Protic Ionic Liquids on Lubricating Steel–Steel and Steel–Aluminum Contacts: Potential Ecofriendly Lubricants and Additives

“…The molecular structures (as shown in Fig. 1) of the three PILs were confirmed from the results of proton nuclear magnetic resonance ( 1 H NMR) characterization which can be found in our previous papers [41,44]. In light of the molecular structures of the three PILs (in Fig.…”

“…In this study, the chemical reagents used to synthesize the PILs were commercially available from Sigma-Aldrich (USA) and used as received without any treatment. The three ecofriendly hexanoate-based protic ionic liquids (PILs) used in this study were prepared in the laboratory according to a procedure published in our previous papers [41,44]. The molecular structures (as shown in Fig.…”

“…In recent studies, Iglesias's research team has designed and synthesized a series of three halogen-free PILs derived from a weak acid with three alkanol amines with different base strengths [41,44]. The ionicity of the three PILs was studied and the lubricating performance of neat PILs and PILs blended with a bio-oil was evaluated in a steel/steel contact.…”

“…The ionicity of the three PILs was studied and the lubricating performance of neat PILs and PILs blended with a bio-oil was evaluated in a steel/steel contact. Experimental results showed that the PIL with the highest ionicity presented the worst tribological behavior when used as neat lubricant, but it performed better when used as an additive to a biodegradable oil [44].…”

Lubricating Properties of Cyano-Based Ionic Liquids against Tetrahedral Amorphous Carbon Film

“…Further, various cations are also being investigated, which include phosphonium and ammonium cations. They increase the solubility of the ionic liquids in the base oils and make it possible to study them as lubricant additives [22][23][24][25]. In addition, very low friction caused by the ionic liquids has been reported in recent years.…”