Abstract

This work explores the tribological properties of choline amino acid protic ionic liquids (PILs) as environmentally friendly lubricants under high temperatures and electrified conditions. These conditions are found in the automotive sector, notably in internal combustion engine vehicles (ICEVs) and electric vehicles (EVs). Lubrication technologies are vital to improving the efficiency and operating lifetime of moving components in automotive drivetrains. The use of ionic liquids (ILs) is actively being researched, with ongoing exploration of their lubricating potential and unique physicochemical characteristics. Compared to traditional petroleum-based lubricants, ILs’ ability to thrive in these conditions will offer substantial benefits, immediately extend operational longevity and potentially have a positive environmental impact. Key properties of ILs include low vapor pressure, high thermal stability, and high molecular polarity. In addition, ILs can form an ordered structure in the liquid state that reduces friction, and if the conditions are appropriate (temperature, load, and speed), the ions of the ILs react with the ions on the metal surface, producing tribo-film layers that can reduce wear. During this investigation, a family of choline amino acid PILs was synthesized using only renewable, biodegradable, and biocompatible products, aligning with the sustainable development goals that address environmental impacts. This family of choline amino acid PILs contains the same choline cation, and amino acids with different side chains for the anions (leucine, isoleucine, aspartic acid, and glycine). They are studied as 1 wt.% additives to a low-viscosity, non-polar polyalphaolefin (PAO) base oil under two separate conditions: elevated temperatures and electrified conditions, under boundary regimes. The tribological testing was performed using a ball-on-flat reciprocating tribometer, with the coefficient of friction (CoF) measured and a wear track generated. Multiple analytical methods characterize the resultant wear tracks, including 3D profilometry, scanning electron microscopy, energy-dispersive x-ray spectroscopy, and Raman spectroscopy. The results revealed that each PAO+PIL mixture exhibited condition-dependent tribological performance. At 100°C, PAO with the choline aspartic acid additive shows reductions in CoF and wear of up to 25% and 42%, respectively, compared to the neat PAO. At high current density (3.0A), PAO with the choline leucine additive shows reductions in CoF and wear of up to 23% and 11%, respectively. The analytical methods identified oxide- and carbon-rich tribofilm, which is attributed to their effectiveness in reducing friction and wear. By advancing more sustainable lubrication solutions, they have the potential to replace conventional lubricants.

Publication Date

6-10-2026

Document Type

Thesis

Student Type

Graduate

Degree Name

Mechanical Engineering (MS)

Department, Program, or Center

Mechanical Engineering

College

Kate Gleason College of Engineering

Advisor

Patricia Iglesias Victoria

Advisor/Committee Member

Alfonso Fuentes Aznar

Advisor/Committee Member

Rui Liu

Campus

RIT – Main Campus

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