Effect of functional groups on tribological properties of lubricants and mechanism investigation

Abstract

Nine organic compounds were utilized as model lubricants to investigate the impact of functional groups on tribological performances. Nonanoic Acid with carboxyl showed the best lubrication properties, and fluid film and tribofilm were coexistent in its friction test, bringing a low friction coefficient and wear rate. In addition, the lubricant with low friction coefficient corresponded to high adsorption energy in density functional theory (DFT) calculations. And the lubricant forming adsorption film with large surface energy displayed small wear rate in friction test. Moreover, adsorption energies positively correlated surface energies. Based on the experimental results, the action mechanism of functional groups on tribological properties of lubricants was proposed. Various functional groups make lubricant molecules show different adsorption energies and surface energies. Lubricant molecules with high adsorption energy are more likely to adsorb on substrates and form a vertical monolayer, which can maintain a regular molecular brush structure during friction and bring a low friction coefficient. And lubricant molecules with high surface energy may be more prone having tribochemical reactions during friction and forming protective tribofilm, which leads to a low wear rate.

CO2 Capture and Conversion into Carbon-Based Tribofilm by In Situ Tribochemical Reaction for Green Lubrication

“…However, pure MEA molecules, due to their lack of charge and weaker interaction with the substrate, cannot form a regular and dense molecular brush structure on the substrate, resulting in higher friction coefficients. At the same time, the stronger interaction between anions with negatively charged carboxylate groups and the substrate also makes carboxylate groups more prone to tribochemical reactions under shear stress and Hertz contact stress, forming a carbon-based tribofilm, which better protects the worn surface and brings lower wear than pure MEA solutions …”

Study of the Effect of ZnO Functionalization on the Performance of a Fully Formulated Engine Oil

“…In particular, a CoF of 0.120 was obtained with a 1.5 wt.% concentration of oleic acid, compared to the reference value of 0.149. This behavior is explained by the absorption of the additive molecule on the steel surfaces, which leads to a lower friction coefficient, and thus, a higher additive concentration [ 45 ].…”

On the Structure–Activity Relationship of Glyceryl oleate Friction Modifiers and Its Synergistic Mechanism on Phosphate ester Antiwear Additives

“…7(a-d). The adsorption energy between the base oil and additive lubrication systems with the metal α-Fe 2 O 3 substrate was calculated according to formula (1) to characterize the interaction between the metal substrate and lubricant molecules [22,25]. E adsroption is the adsorption energy between lubricant molecules and Fe 2 O 3 substrate.…”

“…and hydrocarbon tail chain differences (chain length, saturation, etc.) dominate the tribological characteristics [23][24][25][26].…”

“…Attributed to the formation of a bilayer structure consisting of a chemisorbed layer and a hydrogen bonding network layer on the metal surface by polar head groups. Yu et al [25] explored the in uence of functional group differences of nine additives on tribological properties through friction experiments and DFT calculation. The results indicate that acid additives with carboxyl functional groups exhibit the best friction reduction and antiwear properties, attributed to greater adsorption and surface energy exhibited by the acid additives on metal surfaces.…”