Ionic liquids (ILs) offer multifunctional capabilities as lubricant additives. However, many conventional ILs contain moisture-sensitive halogen-based anions that may hydrolyze to form corrosive halogen acids, leading to surface degradation. This study explored halogen-free, amine-based protic ionic liquids (PILs) as additives in polar base oil polyethylene glycol (PEG200). Anti-corrosion tests revealed that incorporating PILs into PEG200 significantly improves corrosion resistance. Lubrication tests performed at various PIL concentrations showed that the blend containing 5wt% PIL exhibited the best performance, reducing the friction coefficient by 26.12% and wear volume by 90.61% compared to neat PEG200. Spectroscopic analysis confirms the formation of a protective tribofilm within the wear tracks, consisting of oxy-organic compounds and metal oxides such as FeOOH, Fe2O3 and Fe3O4. This tribofilm minimizes direct contact between sliding surfaces and facilitates effective lubrication. These findings demonstrate the potential of amine-based PILs as efficient and environmentally friendly additives for PEG-based lubricants.
LiuCLiZLuW, et al.Reactive wear protection through strong and deformable oxide nanocomposite surfaces. Nat Commun2021; 12: 1–8.
4.
ZengQNingZPangZ, et al.Self-assembled multilayer WS2/GO films on amorphous silicon coating for enhancing the lubricating properties. Appl Surf Sci2023; 624: 157184.
5.
WangYSuHYinJ, et al.Catalytic and tribological performances of a novel bi-functional ionic liquid in lubricating ester oil. Lubricants2025; 13: 1–14.
6.
YeCLiuWChenY, et al.Room-temperature ionic liquids: a novel versatile lubricant. Chem Commun2001; 21: 2244–2245.
7.
RohlmannPBlackJJWatanabeS, et al.Tribochemistry of imidazolium and phosphonium bis(oxalato)borate ionic liquids: understanding the differences. Tribol Int2023; 181: 108263.
8.
InconelA. The tribological properties of low-sulfur and low-phosphorus.
9.
YuQZhangCDongR, et al.Physicochemical and tribological properties of gemini-type halogen-free dicationic ionic liquids. Friction2021; 9: 344–355.
10.
YanJMangoliniF. Polymer-Encapsulated ionic liquids as lubricant additives in non-polar oils. J Mol Liq2023; 383: 122089.
11.
YuBZouKWangR, et al.A novel polyionic liquid with lubricity and viscosity-increasing dual functionalities as the additive in aqueous lubrication system. Friction2024; 12: 698–710.
12.
FanJShenYLiuY, et al.Improved friction and wear performance utilized with aminoguanidine-based ionic liquid over wide temperature range for reciprocating frictional contact surface. Tribol Lett73. Epub ahead of print 2025. DOI: https://doi.org/10.1007/s11249-025-01973-6.
13.
PericBMartíESierraJ, et al.Terrestrial ecotoxicity of short aliphatic protic ionic liquids. Environ Toxicol Chem2011; 30: 2802–2809.
14.
CamargoDAndradeRSFerreiraGA, et al.Investigation of the rheological properties of protic ionic liquids. J Phys Org Chem2016; 29: 604–612.
15.
PericBSierraJMartíE, et al.A comparative study of the terrestrial ecotoxicity of selected protic and aprotic ionic liquids. Chemosphere2014; 108: 418–425.
16.
DonatoMTDeuermeierJColaçoR, et al.New Protic Ionic Liquids as Potential Additives to Lubricate Si-Based MEMS/NEMS. Molecules28. Epub ahead of print 2023. DOI: https://doi.org/10.3390/molecules28062678.
17.
CaiZbMeyerHMMaC, et al.Comparison of the tribological behavior of steel-steel and Si3N4-steel contacts in lubricants with ZDDP or ionic liquid. Wear2014; 319: 172–183.
18.
ViescaJLOulegoPGonzálezR, et al.Miscibility, corrosion and environmental properties of six hexanoate- and sulfonate-based protic ionic liquids. J Mol Liq322. Epub ahead of print 2021. DOI: https://doi.org/10.1016/j.molliq.2020.114561.
19.
PatelAGuoHIglesiasP. Study of the lubricating ability of protic ionic liquid on an aluminum-steel contact. Lubricants6. Epub ahead of print 2018. DOI: https://doi.org/10.3390/lubricants6030066.
20.
KhanAGusainRSahaiM, et al.Fatty acids-derived protic ionic liquids as lubricant additive to synthetic lube base oil for enhancement of tribological properties. J Mol Liq2019; 293: 111444.
21.
GuoHIglesiasP. Tribological behavior of ammonium-based protic ionic liquid as lubricant additive. Friction2021; 9: 169–178.
22.
QuGFangHLiuL, et al.High-performance protic ionic liquids as additives in lubricating oils with varying polarity. Tribol Int191. Epub ahead of print 2024. DOI: https://doi.org/10.1016/j.triboint.2023.109157.
23.
AvilésMDMostazaPBermúdezMD, et al.Epoxidized vegetable lubricant enhanced by ionic liquid. Wear564–565. Epub ahead of print 2025. DOI: https://doi.org/10.1016/j.wear.2025.205740.
24.
XiangJZhengZChenH, et al.Robust Macroscale Superlubricity Enabled by the Protic Ionic Liquid Polyol Aqueous Solution: from Interface Adsorption to Tribofilm Formation. ACS Appl Mater Interfaces. Epub ahead of print 2025. DOI: https://doi.org/10.1021/acsami.4c19237.
25.
BaiZQiuJZhangD, et al.Tribological behavior of 1,8-Diazabicyclo[5.4.0]Undecane-7-Ene–organophosphoric acid-based protic ionic liquids as lubricant additives. Tribol Lett2023; 71: 1–11.
26.
ShiYYangSZhangX, et al.Towards outstanding lubricity performance of proton-type ionic liquids or synergistic effects with friction modifiers used as oil additives at the steel/steel interface. Soft Matter2023; 20: 365–374.
KawadaSWatanabeSKondoY, et al.Tribochemical reactions of ionic liquids under vacuum conditions. Tribol Lett2014; 54: 309–315.
29.
WijanarkoWKhanmohammadiHEspallargasN. Effect of steel hardness and composition on the boundary lubricating behavior of low-viscosity PAO formulated with dodecanoic acid and ionic liquid additives. Langmuir2022; 38: 2777–2792.
30.
AntunesMDonatoMTPazV, et al.Improving the lubrication of silicon surfaces using ionic liquids as oil additives: the effect of Sulfur-based functional groups. Tribol Lett2020; 68: 1–14.
31.
ShangWYeMCaiT, et al.Tuning of the hydrophilicity and hydrophobicity of nitrogen doped carbon dots: a facile approach towards high efficient lubricant nanoadditives. J Mol Liq2018; 266: 65–74.
32.
PatroBDKSuvinPSKreivaitisR, et al.Investigating the Wettability, Rheological, and Tribological Properties of Ammonium-Based Protic Ionic Liquids as Neat Lubricants for Steel–Steel and Steel–Aluminium Contacts. Lubricants11. Epub ahead of print 2023. DOI: https://doi.org/10.3390/lubricants11110469.
33.
DonatoMTSantosLDiogoHP, et al.Eutectic systems containing an ionic liquid and PEG200 as lubricants for silicon surfaces: effect of the mixture's molar ratio. J Mol Liq2022; 350: 118572.
34.
Kumar PatroBDShivakumarSuvinPS, et al.Effect of temperature on tribological behavior of L–proline–based green deep eutectic solvents for Ti6Al4V interfaces: a study of novel potential lubricant. Tribol Int2025; 208: 110667.
35.
SuTSongGZhengD, et al.Facile synthesis of protic ionic liquids hybrid for improving antiwear and anti-corrosion properties of water-glycol. Tribol Int2021; 153: 106660.
36.
DongJSunQZhangS, et al.Synthesis and tribological study of a novel thiadiazole derivative as multifunctional lubricant additive. Colloids Surfaces A Physicochem Eng Asp2025; 707: 135825.
37.
MaRZhaoQZhangE, et al.Synthesis and evaluation of oil-soluble ionic liquids as multifunctional lubricant additives. Tribol Int2020; 151: 106446.
38.
PillariLKLessowayKBichlerL. Reciprocating dry sliding friction and wear behavior of B319 aluminum alloy-graphene composites. Tribol Int2024; 192: 109334.
39.
Usha RaniSKesavanDRamaseshanR, et al.Fretting wear behavior of LPBF ti-6Al-4V alloy: influence of annealing and anodizing. J Tribol2025; 147: 1–12.
40.
BambamAKAlokARajakA, et al.Tribological performance of phosphonium-based halogen-free ionic liquids as lubricant additives. Proc Inst Mech Eng Part J J Eng Tribol2023; 237: 881–893.
41.
XuFTianBCuiK, et al.Fortified lubricating response to sustainable PEG system from protic ionic liquid and their strong hydrogen bonding network. ACS Sustain Chem Eng2024; 12: 5343–5355.
42.
DonatoMTColaçoRBrancoLC, et al.Molecular interactions between ionic liquid lubricants and silica surfaces: an MD simulation study. J Phys Chem B2024; 128: 2559–2568.
43.
StemmerPFischerA. Pathways of dissipation of frictional energy under boundary lubricated sliding wear of martensitic materials. Lubricants6. Epub ahead of print 2018. DOI: https://doi.org/10.3390/lubricants6020034.
44.
de CastroVVMazzini FontouraLABenficaJD, et al.Lubricated sliding wear of SAE 1045 and SAE 52100 steel against alumina in the presence of biodiesel, diesel and a 50:50 blend of those fuels. Wear2016; 368–369: 267–277.
45.
MauryaUVasuV. Boehmite nanoparticles for potential enhancement of tribological performance of lubricants. Wear2022; 498–499: 204311.
46.
LiYLiHFanX, et al.Oil-soluble deep eutectic solvent as high-performance green lubricant additives for PAO 40 and PEG 200. Tribol Int2023; 186: 108602.
47.
NieuwoudtMKCominsJDCukrowskiI. The growth of the passive film on iron in 0.05 M NaOH studied in situ by Raman micro-spectroscopy and electrochemical polarisation. Part I: near-resonance enhancement of the Raman spectra of iron oxide and oxyhydroxide compounds. J Raman Spectrosc2011; 42: 1335–1339.
48.
LeeAPWebbJMaceyDJ, et al.In situ Raman spectroscopic studies of the teeth of the chiton acanthopleura hirtosa. J Biol Inorg Chem1998; 3: 614–619.
49.
Bajt LebanMKosecT. Characterization of corrosion products formed on mild steel in deoxygenated water by Raman spectroscopy and energy dispersive X-ray spectrometry. Eng Fail Anal2017; 79: 940–950.
50.
HuangNShortMZhaoJ, et al.Full range characterization of the Raman spectra of organs in a murine model. Opt Express2011; 19: 22892.
51.
FarberCLiJHagerE, et al.Complementarity of Raman and infrared spectroscopy for structural characterization of plant epicuticular waxes. ACS Omega2019; 4: 3700–3707.
52.
RajARajuKVargheseHT, et al.IR, Raman and SERS spectra of 2-(methoxycarbonylmethylsulfanyl)-3,5-dinitrobenzene carboxylic acid. J Braz Chem Soc2009; 20: 549–559.
53.
LuPChenWFanJ, et al.Thermally triggered nanocapillary encapsulation of lauric acid in polystyrene hollow fibers for efficient thermal energy storage. ACS Sustain Chem Eng2018; 6: 2656–2666.
54.
de CastroVVdos SantosLMAntoniniLM, et al.Water-based lubricant containing protic ionic liquids and talc lubricant particles: Wear and corrosion analysis. Wear518–519. Epub ahead of print 2023. DOI: https://doi.org/10.1016/j.wear.2023.204633.
