**Acknowledgements**

*Tribology in Materials and Manufacturing - Wear, Friction and Lubrication*

PAO 0.14 38.5x10−7 mm3

PAO@1.67% amine-phosphate 0.1 9x10−7 mm3

PAO@ 0.75% [P4444][DEHP] 0.11 2.5x10−7 mm3

PAO@1.03% [P66614][DEHP] 0.08 13x10−7 mm3

PAO@1.65% [P66614][i-C7H15COO] 0.11 4x10−7 mm3

PAO@1.98% [P66614][n-C17H35COO] 0.08 3x10−7 mm3

PAO@ 2.44% [P66614][RSO3] 0.11 7x10−7 mm3

PAO@ 5% P66614 DEHP 0.1 5.6x10−7 mm3

5 W-30 engine oil 0.1 4.7x10−7 mm3

5 W-30 engine oil @ 5% P66614 DEHP 0.1 1.3x10−7 mm3

10 W base oil >0.3 490x10−7 mm3

10 W C 5% PP-IL 0.09 4.7x10−7 mm3

10 W-30 engine oil 0.1 9x10−7 mm3

10 W-30 engine oil C 5% PP-IL 0.11 2.5x10−7 mm3

PEG-200@ 1% MIm5-(BScB)2 0.07 360 mm (wear scar) PEG-200@ 2% MIm5-(BScB)2 0.07 330 mm (wear scar) PEG-200@ 3% MIm5-(BScB)2 0.07 335 mm (wear scar) PAO 0.22 4.9x10−4 mm3

**Lubricants COF Wear Contact Reference**

PEG-200 0.12 730 mm (wear scar) Steel–steel [75]

/Nm Cast

/Nm Cast

/Nm Cast

iron–steel

iron–steel

/Nm

/Nm

/Nm

/Nm

/Nm

/Nm

/Nm

/Nm

/Nm

/Nm

/Nm

/Nm

iron–steel

[46]

[11]

[12]

of oil-miscible quaternary ammonium phosphites ILs as Lubricant additives in PAO is also investigated in different surface environment and shows efficient reduction of wear [53]. Biodegradable fatty-acid-constituted halogen-free ILs are efficient for renewable, environmentally friendly, and high-performance lubricant additives [76]. Halogen-free imidazolium/Ammonium-bis(salicylato)borate ILs act as highperformance lubricant additives and lower wear values on metal surfaces [74]. For better understanding the utility of ILs as lubricant additive in oils, COF and wear

For ILs as lubrication, the major concerns included corrosion, thermal oxidation, oil-miscibility, toxicity, and cost. The recent successful development of noncorrosive, thermally stable, and oil-soluble ILs has largely been addressed and discussed in technical barriers and application point of views. The mainstream research of IL involved lubrication has been shifted from using ILs as neat or base lubricants to using them as lubricant additives. The development of ILs as new lubricating systems are encouraging and still challenging issues in present day. There must be considered the disintegration and corrosion problems of ILs related to their applications as lubricant. However, these fundamental issues can help us to the understanding of fundamental mechanisms of tribology. Now, the focus is to develop halogen and phosphorus-free ILs as energy efficient and

properties are for few ILs and listed in **Table 2**.

*Tribological properties of ILs as lubricant additives.*

**12**

**4. Conclusion**

**Table 2.**

SKP acknowledges Department of Chemistry, Uka Tarsadia University, Maliba Campus, Gopal Vidyanagar, Bardoli, Mahuva Road, Surat-394350, Gujrat, India. Conflict of Interest.
