Elastohydrodynamic Performance of a Bio-Based, Non-Corrosive Ionic Liquid

Abstract

Abstract:To improve performance of machine components, lubrication is one of the most important factors. Especially for use in extreme environments, researchers look for other solutions rather than common lubricant base stocks like mineral oils or vegetable oils. One such example is ionic liquids. Ionic liquids have been defined as molten salts with melting points below 100 • C that are entirely ionic in nature, comprising both cationic and anionic species. The industrial use of ionic liquids is mostly as solvents, electrolytes, extractants and catalysts. In tribological applications, ionic liquids are mainly studied in boundary lubrication and in pure sliding contacts. In this work, the elastohydrodynamic performance of a bio-based, non-corrosive, [choline][L-proline] ionic liquid is evaluated in terms of pressure-viscosity response, film forming capability and friction. The results show a pressure-viscosity coefficient of below 8 GPa −1 at 25 • C, among the lowest reported for any ionic liquid. The ionic liquid generated up to 70% lower friction than a reference paraffin oil with a calculated difference in film thickness of 11%. It was also shown that this ionic liquid is very hygroscopic, which is believed to explain part of the low friction results, but also has to be considered in practical applications since the water content will influence the properties and thus the performance of the lubricant.

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

“…In the recent decade, ionic liquids (ILs) have shown great potential as lubricants [6][7][8][9][10][11][12][13][14] or lubricant additives [15][16][17][18][19][20][21][22][23][24][25][26] due to their excellent physicochemical properties [27,28], including low melting point, low flammability, negligible vaper pressure, and high thermal stability. One of the most important characteristics of ILs is that their properties can be tailored by varying the species of the cations and anions, giving rise to numerous families that can be used across different tribological systems.…”

Temperature Dependence on Density, Viscosity, and Electrical Conductivity of Ionic Liquid 1-Ethyl-3-Methylimidazolium Fluoride

“…Numerous studies have focused on designing new ILs and on the relationship between the phase behavior and molecular structure, in order to clarify the nature of ILs and expand their applications [11][12][13][14][15].…”

Controllable Friction of Green Ionic Liquids via Environmental Humidity

“…An approximation of this parameter for [Cho][Pro] at 25 C is 8.0 GPa À1 , which was computed in the previous work when the water content was lower than 15%. [40] Although we could not get the exact value of pressure-viscosity coefficient with 20%, 25%, and 30% water content, we know that the pressureviscosity coefficient will decrease after adding more water into…”

“…Before getting a basic understanding of the role of humidity in controlling friction, the water adsorption kinetics at different RHs should be studied. Björling et al [40] studied the water adsorption kinetics of [Cho][Pro] at one specific humidity (15% RH). Herein, we studied the absorbed moisture in [Cho][Pro] at different environmental humidities at 25 C (Figure 1).…”

“…[36][37][38][39] We also found that Choline Proline [Cho][Pro] was highly hygroscopic when its elastohydrodynamic performance was investigated. [40] This means that [Cho][Pro] has high potential to be able to capture moisture when used as a lubricant. DOI: 10.1002/adem.201901253 Intelligent control of friction is an attractive but challenging topic.…”