Session: 13-11-03: Friction, Fracture, and Damage III

Paper Number: 165379

Tribological Performance of Choline Amino Acid Protic Ionic Liquids as Additives to a Low Viscosity Non-Polar Oil in Steel-Steel Contacts 

Wear and friction in mechanical systems account for nearly a quarter of worldwide energy losses, which is one of the major contributors to energy losses and CO₂ emissions. Advanced lubricant compositions that reduce friction losses present the opportunity to reduce environmental impact and increase energy efficiency. Ionic liquids (ILs), particularly protic ionic liquids (PILs), have drawn interest due to their anti- friction and wear properties and can be designed to avoid toxic halogen elements. Their physicochemical characteristics, such as high thermal stability, configurable polarity, and inherent lubricity, have made them attractive candidates. This study investigates the tribological performance of three choline-based amino acid PILs (CHAAPILs)—choline-leucine ([CHO][LEU]), choline-isoleucine ([CHO][ILEU]), and choline-aspartic acid ([CHO][ASP])—as additives to polyalphaolefin (PAO), a commercially available ultra-low viscosity non-polar base oil.

Tribological experiments were conducted under boundary lubrication conditions using a reciprocating ball-on-disk tribometer. Both the disk and the ball were made of 52100 steel, and the tests were conducted under a 3 N load. The lubricating efficiency of each lubricant was assessed by measuring its wear volume and coefficient of friction (COF). The wear mechanisms were characterized using an optical microscope by assessing the images of the wear tracks and calculating the wear volume. A profilometer was used to characterize the surface topography. To determine the tribo-chemical reactions that occur on the worn surfaces and to shed light on the underlying wear mechanisms, additional characterizations were performed using energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), and Raman spectroscopy.

Results revealed that adding just 1 wt.% of the CHAAPILs to PAO reduced COF, with PAO+[CHO][ASP] achieving the highest friction reduction of approximately 26%. The amino acid anion structure had a significant impact on the wear performance, with PAO+[CHO][ASP] exhibiting the lowest wear volume because of its stronger polarity and ability to build protective surface layers. On the other hand, lubrication with PAO+[CHO][LEU] resulted in a slight rise in wear volume despite reducing COF, suggesting that the molecular makeup of the amino acid anion is a key factor in defining anti-wear characteristics.

Post-test surface characterization using optical microscopy, profilometry, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Raman spectroscopy provided insight into the wear mechanisms associated with each lubricant. The superior tribological performance of PAO+[CHO][ASP] was linked to the formation of a protective tribo-chemical film on the steel surface. By combining various surface analysis approaches, this research attempts to correlate reported friction and wear characteristics with the lubricating action of PILs as additives.

The findings advance the knowledge of how IL-based lubricants interact with steel surfaces and help shape the creation of eco-friendly lubrication techniques for non-polar base oils. Furthermore, these results highlight the potential of CHAAPILs as environmentally acceptable, bio-derived additives for non-polar lubricants that provide anti-wear and friction reduction advantages. The findings support the continuous advancement of environmentally friendly lubricating technology meant to reduce CO₂ emissions and energy losses in mechanical systems.

Presenting Author: Davis Kiboi Rochester Institute of Technology

Presenting Author Biography: Davis Kiboi is a PhD student and Graduate Research Assistant in the Department of Mechanical Engineering at Rochester Institute of Technology. His research focuses on understanding the lubrication mechanisms of environmentally compatible lubricants for sustainable tribological applications. His current work explores the physicochemical properties, tribological performance, and lubrication mechanisms of ionic liquids as neat lubricants and lubricant additives in both polar and non-polar base oils and for various mechanical systems.

He has authored multiple publications on the tribological performance of choline-based ionic liquids, with a particular focus on their potential as green alternatives to conventional lubricants. His research interests include green lubricants, ionic liquids, tribo-chemistry, and surface interactions in lubricated contacts.

He is a member of the American Society of Mechanical Engineers (ASME).

Authors:

Davis Kiboi Rochester Institute of Technology
Esmond Lau Rochester Institute of Technology
Michael Coleman SUNY Brockport
Filippo Mangolini University of Texas at Austin
Patricia Iglesias Rochester Institute of Technology