New Developments and Future Trends of Ionic Liquids as Lubricants

A special issue of Lubricants (ISSN 2075-4442).

Deadline for manuscript submissions: closed (20 October 2023) | Viewed by 10662

Special Issue Editors

Department of Mechanical Engineering, Kate Gleason College of Engineering, Rochester Institute of Technology, Rochester, NY 14623, USA
Interests: friction; wear; lubrication; ordered fluids; textured surfaces; 3D metals
Development Engineering of HDD, Western Digital, San Jose, CA 95119, USA
Interests: ionic liquids; boundary lubrication; friction; wear; nanotribology; tribochemistry

Special Issue Information

Dear Colleagues,

Since 2001, when the first paper on the use of ionic liquids (ILs) as lubricants was published, the interest in these ordered fluids has increased rapidly in the tribology community. ILs are low-melting-point salts with unique and tunable physicochemical properties. Their non-flammability, negligible volatility, good thermal stability, and wide liquid range make them ideal candidates for lubricant applications. In addition, their high polarity may promote the formation of effective adsorption films or tribolayers on the surfaces in contact, resulting in important friction and wear reductions. The purpose of this Special Issue is to summarize the latest developments and future trends in the field of ionic liquids as lubricants and additives. The main topics of interest include, but are not limited to:

  • Ionic liquids as high-performance neat lubricants;
  • Ionic liquids as additives to lubricants;
  • Biodegradability and miscibility of ionic liquids;
  • Ionic liquids as green lubricants/additives;
  • Ionic liquids for high-temperature applications.

Dr. Patricia Iglesias
Dr. Hong Guo
Guest Editors

Manuscript Submission Information

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Keywords

  • ionic liquids
  • friction
  • wear
  • lubrication
  • additives
  • tribochemistry
  • biolubricants

Published Papers (6 papers)

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Research

11 pages, 4883 KiB  
Article
Tribological Properties of Protic Ionic Liquid as an Additive in Aqueous Glycerol Solution for Ruby-Bearing Steel Tribo-Contact
by Raimondas Kreivaitis, Milda Gumbytė, Artūras Kupčinskas, Jolanta Treinytė and Albinas Andriušis
Lubricants 2023, 11(1), 34; https://0-doi-org.brum.beds.ac.uk/10.3390/lubricants11010034 - 16 Jan 2023
Cited by 2 | Viewed by 1415
Abstract
Owing to their low cost and environmentally friendly nature, water-based lubricants have benefits over oil-based ones. However, the appropriate additive package is indispensable in improving its tribological properties. In the current study, we have investigated the friction and wear reduction ability of bis(2-hydroxyethyl) [...] Read more.
Owing to their low cost and environmentally friendly nature, water-based lubricants have benefits over oil-based ones. However, the appropriate additive package is indispensable in improving its tribological properties. In the current study, we have investigated the friction and wear reduction ability of bis(2-hydroxyethyl) ammonium oleate protic ionic liquid (PIL) in a glycerol aqueous lubricating fluid. The tribo-tests were performed using a ruby–steel friction pair acting in reciprocation mode. The coefficient of friction and wear were the main characteristics of the evaluation. Analysis of the physical properties of the investigated lubricating samples and worn surface analysis were performed to reveal a more detailed picture. The study shows that the investigated PIL can significantly reduce friction and wear. The most suitable concentration of PIL was 0.5%, where friction and wear were reduced 2.6 and 15.8 times, respectively. Using the investigated PIL facilitates a sliding coefficient of friction as low as 0.039. It was hypothesized that the formation of the adsorption layer and metal soap was responsible for this. Further studies could be directed toward higher load and speed applications. Full article
(This article belongs to the Special Issue New Developments and Future Trends of Ionic Liquids as Lubricants)
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13 pages, 9213 KiB  
Communication
Triprotic Ammonium Oleate Ionic Liquid Crystal Lubricant for Copper-Copper Friction and Wear Reduction
by María-Dolores Avilés, Ana-Eva Jiménez, Ramón Pamies, Francisco-José Carrión-Vilches and María-Dolores Bermúdez
Lubricants 2022, 10(11), 290; https://0-doi-org.brum.beds.ac.uk/10.3390/lubricants10110290 - 01 Nov 2022
Cited by 2 | Viewed by 1236
Abstract
The triprotic ammonium carboxylate ionic liquid crystal (2-hydroxyethyl)ammonium oleate (MO) has been studied as a neat lubricant and as a lubricant additive in two base oils, PAO6 and 100N. The lubricants have been used in commercially pure copper-OFHC copper balls on disk reciprocating [...] Read more.
The triprotic ammonium carboxylate ionic liquid crystal (2-hydroxyethyl)ammonium oleate (MO) has been studied as a neat lubricant and as a lubricant additive in two base oils, PAO6 and 100N. The lubricants have been used in commercially pure copper-OFHC copper balls on disk reciprocating sliding contact at room temperature. Neat MO presents a very good lubricating performance, with a friction coefficient of 0.06 and a wear rate of OFHC copper disk of 4.15 × 10−7 mm3/N·m. These results are, respectively, 94% and 98% lower than those obtained for PAO6, with similar reductions obtained with respect to 100N. MO has also been studied as an additive in 2wt.% proportion. The severe abrasive wear mechanism that takes place in the presence of neat base oils is reduced by the MO additive. Full article
(This article belongs to the Special Issue New Developments and Future Trends of Ionic Liquids as Lubricants)
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15 pages, 12827 KiB  
Article
Tribological Properties of Borate-Based Protic Ionic Liquids as Neat Lubricants and Biolubricant Additives for Steel-Steel Contact
by Alfonso Sierra, Michael G. Coleman and Patricia Iglesias
Lubricants 2022, 10(10), 269; https://0-doi-org.brum.beds.ac.uk/10.3390/lubricants10100269 - 19 Oct 2022
Cited by 1 | Viewed by 2098
Abstract
A series of four novel halogen-free borate-based protic ionic liquids were synthesized with identical organoborate anions but dissimilar ammonium cations, to allow systematic discussion of the effects of cation alkyl chain group length on their physicochemical and tribological properties. The ionic liquids (ILs) [...] Read more.
A series of four novel halogen-free borate-based protic ionic liquids were synthesized with identical organoborate anions but dissimilar ammonium cations, to allow systematic discussion of the effects of cation alkyl chain group length on their physicochemical and tribological properties. The ionic liquids (ILs) studied showed up to a 30% friction reduction compared to a biolubricant and even displayed negligible wear when tested as neat lubricants. Blends of 1 wt.% ionic liquid and biolubricant were also investigated, leading up to maximum friction and wear reductions of 25% and 96%, respectively, compared to the base oil. Interestingly, the ionic liquid that performed least effectively as a neat lubricant due to the solidification of the fluid achieved the best tribological response as a lubricant additive. The tribological improvements were attributed to the formation of a self-assembled adsorbed layer that separated the frictional surfaces. This theory was supported by rheological studies and elemental analysis. Full article
(This article belongs to the Special Issue New Developments and Future Trends of Ionic Liquids as Lubricants)
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15 pages, 5949 KiB  
Article
Elaboration of Ionic Liquids on the Anti-Wear Performance of the Reinforced Steel-Steel Contact Surface
by Hua Jiang, Xianjun Hou, Yuxin Ma, Weiwei Guan, Haijun Liu and Yucong Qian
Lubricants 2022, 10(10), 260; https://0-doi-org.brum.beds.ac.uk/10.3390/lubricants10100260 - 14 Oct 2022
Cited by 3 | Viewed by 1284
Abstract
This study conducted a tribological investigation of base oil (PAO6 and 5W 40) and ionic liquids (IL)-modified lubricants through a four-ball tribometer for 30 min. The lubricants were fabricated via a two-step method using stirring magnetic and ultrasonic dispersion. IL, base oil, and [...] Read more.
This study conducted a tribological investigation of base oil (PAO6 and 5W 40) and ionic liquids (IL)-modified lubricants through a four-ball tribometer for 30 min. The lubricants were fabricated via a two-step method using stirring magnetic and ultrasonic dispersion. IL, base oil, and lubricants were, respectively, characterized by XRD and FTIR analysis. In addition, multiple characterizations such as EDS, 3D morphology, and SEM were carried out to evaluate the wear and friction performance of steel balls. Ultimately, the results showed that the coefficient of friction (COF) and wear scar diameter (WSD) of wear scar lubricated by IL-modified lubricants were greatly decreased than that by base oil. IL can well improve the tribological properties of PAO 6 oil and 5W-40 oil due to the tribo-film appearance on the friction surface of wear scar by the effective role of IL. Fascinatingly, this investigation comprehensively and elaborately put a new sight into the lubrication mechanism of how IL reacted with a base oil and enhanced the tribological characteristics. Full article
(This article belongs to the Special Issue New Developments and Future Trends of Ionic Liquids as Lubricants)
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16 pages, 12626 KiB  
Article
New Water-Ethylene Glycol Lubricants with Stearate Ionic Liquid Crystal Additive
by María-Dolores Avilés, Cristian Sánchez-Rodríguez, Ramón Pamies, María-Dolores Bermúdez, Francisco-José Carrión-Vilches, Susana García Sanfelix and Anna-Lena Kjøniksen
Lubricants 2022, 10(10), 241; https://0-doi-org.brum.beds.ac.uk/10.3390/lubricants10100241 - 28 Sep 2022
Cited by 4 | Viewed by 1760
Abstract
The main purpose of the present study is to improve the tribological performance of aqueous lubricants with the use of ecofriendly, fatty acid-derived additives. The protic ionic liquid crystal bis(2-hydroxyethyl)ammonium stearate (DES) has been added to 50:50 water+ethylene glycol (W–EG) to obtain (W–EG)+0.5%DES; [...] Read more.
The main purpose of the present study is to improve the tribological performance of aqueous lubricants with the use of ecofriendly, fatty acid-derived additives. The protic ionic liquid crystal bis(2-hydroxyethyl)ammonium stearate (DES) has been added to 50:50 water+ethylene glycol (W–EG) to obtain (W–EG)+0.5%DES; (W–EG)+1%DES and (W–EG)+2%DES emulsions. The new lubricants have been studied in sapphire-AISI (American Iron and Steel Institute) 316L stainless-steel pin-on-disk sliding contacts. The addition of DES reduces the friction coefficient by up to 76% and wear rate by up to 80%, with respect to (W–EG). The best performance is found for the emulsions with the lower proportion of DES (0.5 and 1 wt.%). These results have been related to viscosity and turbidity values. Wear mechanisms have been studied by Scanning Electron Microscopy/Energy Dispersive X-ray Spectroscopy (SEM/EDX) and by Raman microscopy. While W–EG shows a severe abrasive mechanism, no abrasion marks are present inside the wear track after lubrication with (W–EG)+0.5%DES, the emulsion with the lowest wear rate. After lubrication with W–EG, an increase in oxygen content is observed inside the wear track, as determined by EDX and confirmed by Raman microscopy, which shows the presence of iron oxides. The addition of DES reduces these oxidation processes. Full article
(This article belongs to the Special Issue New Developments and Future Trends of Ionic Liquids as Lubricants)
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15 pages, 4906 KiB  
Article
Methyltrioctylammonium Octadecanoate as Lubricant Additive to Different Base Oils
by Javier Faes, Rubén González, David Blanco, Alfonso Fernández-González, Antolin Hernández-Battez, Patricia Iglesias and José Luis Viesca
Lubricants 2022, 10(6), 128; https://0-doi-org.brum.beds.ac.uk/10.3390/lubricants10060128 - 17 Jun 2022
Cited by 2 | Viewed by 1764
Abstract
This study investigates the use of an ionic liquid obtained from fatty acids (FAIL) as an additive at 2 wt.% in two different base oils: a mineral oil (M1) and a polyol ester (E1). Physicochemical characterization of the base oil–FAIL blends confirmed the [...] Read more.
This study investigates the use of an ionic liquid obtained from fatty acids (FAIL) as an additive at 2 wt.% in two different base oils: a mineral oil (M1) and a polyol ester (E1). Physicochemical characterization of the base oil–FAIL blends confirmed the miscibility of the FAIL in the base oils. The addition of the FAIL hardly changed the density of the base oils and the viscosity slightly increased at lower temperatures. The tribological performance of the base oils and their blends with the FAIL was determined using three different tests: Stribeck curve determination and tribofilm formation tests, both under sliding/rolling motion, and reciprocating wear tests. The M1 + FAIL blend showed the lowest friction values under the mixed lubrication regime due to its higher viscosity, while the E1 + FAIL showed the lowest friction values under the elastohydrodynamic lubrication regime, which may well have been due to its higher polarity. Only the E1 + FAIL blend outperformed the antiwear behavior of the base oil, probably because it has better chemical affinity (higher polarity) for the metallic surface. SEM images showed that the predominant wear mechanism was adhesive-type with plastic deformation and XPS studies proved that the presence of increasing amounts of organic oxygen on the wear scar caused better antiwear performance when the E1 + FAIL blend was used. Full article
(This article belongs to the Special Issue New Developments and Future Trends of Ionic Liquids as Lubricants)
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