The impact of organic friction modifiers on engine oil tribofilms

Organic friction modifiers (OFMs) are important additives in the lubrication of machines and especially of car engines where performance improvements are constantly sought-after. Together with zinc dialkyldithiophosphates (ZDDPs) antiwear additives, OFMs have a predominant impact on the tribological behaviour of the lubricant. In the current study, the influence of OFMs on the generation, tribological properties and chemistry of ZDDP tribofilms has been investigated by combining tribological experiments (MTM) with in-situ film thickness measurements through optical interference imaging (SLIM), Alicona profilometry and X-ray photoelectron spectroscopy. OFMs and antiwear additives have been found to competitively react/adsorb on the rubbing ferrous substrates in a tribological contact. The formation and removal (through wear) of tribofilms are dynamic processes which result from the simultaneous interaction of these two additives with the surface of the wear track. By carefully selecting the chemistry of OFMs, the formulator can achieve lubricants that generate ZDDP antiwear films of optimum thickness, morphology and friction according to the application-specific requirements. <br/

Boundary Lubrication of Oxide Surfaces by Poly(L-lysine)- g -poly(ethylene glycol) (PLL- g -PEG) in Aqueous Media

In this work, we have explored the application of poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG) as an additive to improve the lubricating properties of water for metal-oxide-based tribo-systems. The adsorption behavior of the polymer onto both silicon oxide and iron oxide has been characterized by optical waveguide lightmode spectroscopy (OWLS). Several tribological approaches, including ultra-thin-film interferometry, the mini traction machine (MTM), and pin-on-disk tribometry, have been employed to characterize the frictional properties of the oxide tribo-systems in various contact regimes. The polymer appears to form a protective layer on the tribological interface in aqueous buffer solution and improves both the load-carrying and boundary-layer-lubrication properties of wate

Tungsten dichalcogenide lubricant nanoadditives for demanding applications

Tungsten dichalcogenides such as WS2 and WSe2 have remarkable friction reducing properties in tribological applications due to their layered structure which exfoliates easily under shear. 2H-WS2 nanoparticles (NPs) have recently been shown to possess excellent antiwear properties in high temperature applications due to their ability to react with the steel substrate and generate a chemical tribofilm with very good mechanical properties. Moreover, 2H-WS2 sheets can adhere to the chemical tribofilm and thus also reduce boundary friction. This study investigated the tribological properties of tungsten dichalcogenide NPs with different morphologies (IF and 2H) in high temperature, high pressure test conditions, the aim being to identify their mechanism of action and the differences in their performance. Tribological tests and analysis of tribofilms on the wear tracks revealed that the three additives show a similar mechanism of action based on their chemical reaction with the wear track. However, 2H-WS2 NPs have superior friction reducing and antiwear properties due to their increased reactivity, resulting in a tribofilm that grows faster, thicker, more uniform and richer in tungsten compounds. <br/

The lubricant film-forming properties of modern fire resistant hydraulic fluids

Fire resistant hydraulic fluids tend to show significantly poorer ribological performance in hydraulic systems than conventional mineral oil-based fluids. There have recently been performance problems associated with increases of operating temperatures of mining hydraulics. This paper describes measurements of the elastohydrodynamic and boundary film-forming properties of a range of different hydraulic fluid types at temperatures up to 80°C. These are compared with friction and wear results obtained using the same fluids.<br/

Molecular scale liquid lubricating films

A number of recently-developed experimental techniques, such as force balance, atomic force microscopy and ultrathin film interferometry have enabled the direct study of the properties of very thin liquid lubricating films between solid surfaces. These have been used to demonstrate the structure and rheology, and thus the lubricating ability, of monolayer additive films in rolling and sliding contacts. They have also been used to investigate the thin film properties of simple, additive-free fluids such as hydrocarbon base stocks.This paper reviews previous work on the thin film-forming properties of simple lubricant base fluids. Newwork is carried out using ultrathin film interferometry and a rolling-sliding friction test apparatus. It is found that the quasi-spherical molecules, cyclohexane and OMCTS form enhanced film thicknesses in high pressure, slow speed, rolling contacts. There is also an indication of a step-wise dependence of film thickness on rolling speed, in accord with finding using atomic force microscopy and surface forces apparatus. Friction measurements in mixed rolling-sliding show that these fluids also reduce friction in the boundary film regime

Impact of lung surfactant on wettability and cytotoxicity of nanoparticles

The importance of nanoparticle characterization for nanotoxicology has been extensively emphasized and it has been universally agreed that the most important parameters for characterizing nanomaterials are specific surface area and surface properties (chemistry, hydro-philicity/phobicity, charge etc.). This study is proposing the use of enthalpy of wetting which depends on both specific surface area and surface properties, is easily measurable and proves to be highly relevant for predicting nanoparticles' dispersion state and their interaction with the lungs. It also shows the conditioning effect of the lung surfactant main component, DPPC on the surface of particles when used in concentrations which mimic pulmonary exposure more closely

Dataset for Tungsten dichalcogenide lubricant nanoadditives for demanding applications

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WS2 nanoparticles - potential replacement for ZDDP and friction modifier additives

In high-pressure, high-temperature sliding contacts, WS2 nanoadditives react with the metal substrate to generate 100+ nm chemical tribofilms with a layered structure and excellent tribological properties. The friction, wear and micromechanical properties of WS2 tribofilms are compared with those of tribofilms formed by the zinc dialkyldithiophosphate (ZDDP) antiwear additive and ZDDP-organic friction modifier (OFM) mixture. Nanoindentation measurements showed that WS2 generates tribofilms with higher values of hardness and Young’s modulus than ZDDP and ZDDP+OFM, which explains its excellent antiwear properties. The friction performance of WS2 surpassed that of ZDDP+OFM. The striking reduction of boundary friction is credited to the layered structure of the WS2 tribofilm, with exfoliated /squashed WS2 nanoparticles that fill the gaps and cover the reacted tribofilm. In view of these results, WS2 proves to be a suitable candidate for the replacement of problematic lubricant additives currently in us