Session: Government Agency Student Posters

Paper Number: 173790

Physicochemical Characterization of Choline–amino Acid Protic Ionic Liquids for Lubrication Applications 

Protic ionic liquids (PILs) derived from naturally occurring choline and amino acids are increasingly gaining attention as promising candidates for sustainable and high-performance lubricants. Their tunable molecular structures, environmental compatibility, and multifunctional properties make them attractive for use as neat lubricants or lubricant additives. This study investigates the physicochemical properties of ten choline–amino acid protic ionic liquids (ChAAPILs) to evaluate their potential applicability in tribological systems and base oil formulations.

The main goal of this study is to systematically characterize and compare the physicochemical behavior of ten structurally distinct ChAAPILs, with a focus on key properties that influence lubricant performance and formulation compatibility. Specifically, the study aims to determine the ionic conductivity, viscosity, and thermal stability of each PIL, assess their surface wettability and corrosion interaction with metallic surfaces, and evaluate their miscibility in a range of base oils representing different polarities. By investigating these properties, the study seeks to identify structure–property relationships that guide the rational design and selection of PILs for tribological applications.

Evaluating corrosion is crucial when developing and selecting lubricants, especially those intended for use in direct contact with metal surfaces. Corrosive lubricants can degrade metal components over time, leading to material loss, compromised mechanical integrity, and ultimately system failure. In the context of ionic liquids, even those derived from biocompatible sources, certain anions or pH imbalances can induce aggressive reactions with metals like copper or steel. Therefore, assessing the corrosion behavior of new lubricant candidates ensures their long-term compatibility with engineering materials, prevents costly maintenance or downtime, and supports the development of reliable and sustainable tribological systems.

The ChAaPILs were synthesized via a simple acid–base neutralization reaction between choline hydroxide and ten different amino acids, followed by water removal under reduced pressure. The resulting PILs include combinations of choline with glycine, alanine, lysine, leucine, isoleucine, aspartic acid, proline, histidine, phenylalanine and tyrosine. Each PIL was characterized using a set of techniques. Ionic conductivity was measured using a conductivity meter at controlled temperatures, and viscosity was determined using a rheometer. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to study thermal decomposition profiles and phase transitions. Wettability was assessed by static contact angle measurements on 52100 steel and 6061 aluminum substrates. Corrosion behavior was evaluated on copper samples, followed by visual inspection, mass loss measurements, and spectroscopic evaluation. Miscibility tests were carried out by blending 1 wt.% of each PIL into different base oils and visually evaluating homogeneity and phase stability over time.

The experimental results reveal significant variation in the physicochemical properties of the PILs depending on the side chain structure and functional groups of the amino acid anion. Viscosity measurements showed that PILs with small and nonpolar amino acids exhibited relatively low viscosities at room temperature, while those with bulkier or aromatic residues were markedly more viscous. DSC analysis revealed that most PILs remain liquid over a broad temperature range, with glass transition temperatures (T_g) well below room temperature. TGA data indicated excellent thermal stability.

Wettability analysis showed that most PILs display excellent spreading on metal surfaces suggesting good interfacial compatibility with metal surfaces, which is important for film formation and boundary lubrication.

Together with miscibility and corrosion evaluation, this comprehensive analysis reveals that the physicochemical properties of ChAAPILs can be finely tuned by selecting appropriate amino acids. Future work will explore tribological performance tests under controlled friction and wear conditions, as well as additive synergy with existing commercial base oils.

Presenting Author: Davis Kiboi Rochester Institute of Technology

Presenting Author Biography: Davis Kiboi is a PhD student and Graduate Research Assistant in Mechanical Engineering Department, Rochester Institute of Technology. His research focuses on the lubrication mechanisms of environmentally compatible protic ionic liquids (PILs) for sustainable tribological applications. He investigates the physicochemical properties and performance of PILs as neat lubricants and additives in polar and non-polar base oils. He has authored work on choline-based ionic liquids, highlighting their potential as green alternatives to conventional lubricants. His interests include green lubricants, ionic liquids, tribochemistry, and surface interactions.

Authors:

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