| CHEN Qiang,QIN Jian,LIU Xiao,GUO Pingxia,CAI Meirong,ZHOU Feng.Research Progress of Oil Soluble Ionic Liquids as the Lubricant Additives:From Structure Design to Engineering Application[J],54(9):43-69 |
| Research Progress of Oil Soluble Ionic Liquids as the Lubricant Additives:From Structure Design to Engineering Application |
| Received:February 28, 2025 Revised:April 17, 2025 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2025.09.004 |
| KeyWord:oil soluble ionic liquid lubricant additive anti-friction and anti-wear multifunctional |
| Author | Institution |
| CHEN Qiang |
Shandong Laboratory of Advanced Materials and Green Manufacturing at Yantai, Shandong Yantai , China |
| QIN Jian |
Shandong Laboratory of Advanced Materials and Green Manufacturing at Yantai, Shandong Yantai , China |
| LIU Xiao |
Shandong Laboratory of Advanced Materials and Green Manufacturing at Yantai, Shandong Yantai , China |
| GUO Pingxia |
Shandong Laboratory of Advanced Materials and Green Manufacturing at Yantai, Shandong Yantai , China |
| CAI Meirong |
Shandong Laboratory of Advanced Materials and Green Manufacturing at Yantai, Shandong Yantai , China;State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou , China |
| ZHOU Feng |
State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou , China |
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| Abstract: |
| Since ionic liquids, known for their outstanding physicochemical properties, tribological performance, and relatively low environmental toxicity, were first explored as lubricants in 2001, they have experienced significant advancements in the field of lubrication. Compared to ionic liquids used as neat lubricants, ionic liquid lubricant additives exhibit high efficiency in enhancing the tribological properties of base oils while reducing production costs, making them a practical alternative to conventional lubricant additives. Among the reported ionic liquids utilized as lubricant additives, quaternary phosphorus and ammonium salt ionic liquids have garnered considerable attention due to their excellent oil solubility and lubrication characteristics, which stems from their unique three-dimensional quaternary structures. To elucidate the research progress of oil soluble ionic liquids and inspire the design of more effective lubricant additives, the reported oil soluble quaternary phosphorus, quaternary ammonium salts, and multifunctional ionic liquids since the introduction of the first oil soluble ionic liquid in 2001 are summarized. The effects of the molecular structure of ionic liquids on their oil solubility, thermal stability, and tribological properties are discussed in detail. Furthermore, the lubricating performance differences between quaternary phosphorus and ammonium ionic liquids are investigated, and the traditional lubricant additive ZDDP under various operating conditions are reviewed. Examples evaluating the compatibility of quaternary phosphorus and ammonium salt ionic liquids with traditional additives such as ZDDP and organic molybdenum compounds are also included. These findings indicate that, in most cases, quaternary phosphorus ionic liquids demonstrate superior thermal stability, oil solubility, and lubrication properties compared to their corresponding ammonium salt counterparts. Protic ammonium salt ionic liquids exhibit improved onset decomposition temperature, friction, and wear reduction properties compared to aprotic ones. Additionally, the anion type of synthesized ionic liquids significantly affects their tribological behavior. When ionic liquids share the same cation, the effectiveness ranking for wear protection by anions is organophosphate > carboxylate > sulfonate. Conversely, ionic liquids with sulfonate anions display higher thermal stability than those based on organophosphates, while those with carboxylate anions show the lowest thermal stability. In addition to conventional quaternary phosphorus and ammonium ionic liquids, diverse multifunctional lubricant additives containing quaternary phosphorus and ammonium ionic liquid moieties have been developed to reduce the variety of employed lubricant additives and mitigate potential "antagonistic effects" among them. Generally, these additives not only exhibit excellent anti-friction and wear reduction properties but also demonstrate enhanced detergency, antioxidation, viscosity, or corrosion resistance. More importantly, the functional groups within multifunctional lubricant additives can work synergistically, leading to improved overall lubrication performance. Over the past decade, numerous exceptional oil soluble ionic liquid additives have been reported, benefiting from their tunable structures. Nevertheless, unresolved issues and challenges still remain, including the replacement of traditional lubricant additives, the development of more efficient lubricant systems, and conformity with lubrication requirements under varied and harsh operating conditions. By addressing these challenges and considering the research progress on ionic liquids, this review concludes by proposing a potential solution of developing oil soluble ionic liquid lubricant additives with multifunctional properties. |
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