Competitive Adsorption of Ionic Liquids Versus Friction Modifier and Anti-Wear Additive at Solid/Lubricant Interface—Speciation with Vibrational Sum Frequency Generation Spectroscopy

Abstract

A modern lubricant contains various additives with different functionalities and the interactions or reactions between these additives could induce synergistic or antagonistic effects in tribological performance. In this study, sum frequency generation (SFG) spectroscopy was used to investigate competitive adsorption of lubricant additives at a solid/base oil interface. A silica substrate was used as a model solid surface. The lubricant additives studied here included two oil-soluble ionic liquids (ILs, [N888H][DEHP] and [P8888][DEHP]), an antiwear additive (secondary ZDDP), an organic friction modifier (OFM), and a dispersant (PIBSI). Our results showed that for mixtures of ZDDP and IL in a base oil (PAO4), the silica surface is dominated by the IL molecules. In the cases of base oils containing OFM and IL, the silica/lubricant interface is dominated by OFM over [N888H][DEHP], while it is preferentially occupied by [P8888][DEHP] over OFM. The presence of PIBSI in the mixture of PAO4 and IL leads to the formation of a mixed surface layer at the silica surface with PIBSI as a major component. The SFG results in this investigation provide fundamental insights that are helpful to design the formulation of new lubricant additives of desired properties.

Elucidating Interfacial Chain Conformation of Superhydrophilic Polymer Brushes by Vibrational Sum Frequency Generation Spectroscopy

“…The RH dependence of conformation changes was studied by irradiating the probe beams from the air side of the substrate and detecting the SFG signal in the reflection mode. The polymer brush conformation in liquid water was probed in the reflection mode from the substrate side . The stretch modes of CH 2 , CH 3 , and OH groups were detected.…”

Modeling of Formation and Removal of ZDDP Tribofilm on Rough Surfaces

“…kinds of additives, such as dispersants and viscosity improvers. These additives will compete with ZDDP to adsorb on the sliding surfaces [42], slowing down the formation of ZDDP tribofilm. This may explain why the real liner surface has more wear compared to the modeling surface near the TDC.…”

Effect of an Aftermarket Additive in Powertrain Wear and Fuel Consumption of Small-Capacity Motorcycles: A Lab and Field Study

“…Therefore, the existence of products that improve fuel economy, reduce friction and wear, that are also compatible with any powertrain and commercial lubricant, as assured by metal conditioner manufacturers, is highly promising [2][3][4]. However, the use of products not tested by original equipment manufacturing (OEM) leads to insurance loss, and the evaluation of such products is costly and time-consuming [9,12,13,19,24]. This prevents the faster development of lubricating oils since they are restricted in the hands of a few corporations.…”

“…In addition, the incorporation of additives into the fully formulated oil might change its performance due to mutual interactions between the additives [9,12,18,23]. The synergistic and competitive effects among additives is a major tribology field of research since the wear resistance provided by lubricants is not always directly correlated with an increase in antiwear additives content or friction reduction [18,19,22,23]. In fact, the presented surface analysis did indicate tribofilm formation with different compositions when MC was added to the engine oil (Figures 6-10), suggesting the MC changes the actuation of the mechanisms of the commercial 10W-30.…”

“…Surprisingly, to the best of the authors' knowledge, there was no peer-reviewed reference about MC performance in powertrains, even though that is its primary application. Contrastingly, there are thousands of papers evaluating the performance of base or fully formulated oils with the addition of additives or nanoparticles using standardized and tribological tests [11,[18][19][20][21][22]. Although lab tests (pin-on-disk, four-ball, copper corrosion, etc.)…”