Importance of the catalytic effect of the substrate in the functionality of lubricant additives: the case of molybdenum dithiocarbamates. (August 2021)

• Record Type: Journal Article
• Authors: Peeters, S.; Charrin, C.; Duron, I.; Loehlé, S.; Thiebaut, B.; Righi, M.C.
• Is Part Of: Materials today chemistry. Volume 21(2021)
• Publication Date: 2021-08
• Subjects: MoDTC -- QM/MM simulations -- Tribochemistry -- Lubricant additives -- Friction modifiers -- MoS2; Chemistry -- Periodicals; Materials -- Research -- Periodicals; Materials science -- Periodicals; Chemistry; Materials -- Research; Electronic journals; Periodicals; 660.282
• DOI: 10.1016/j.mtchem.2021.100487
• Languages: English
• ISSNs: 2468-5194

Abstract

Abstract: Molybdenum dithiocarbamates (MoDTCs) are lubricant additives very efficient in reducing the friction of steel, and they are used in a number of industrial applications. The functionality of these additives is ruled by the chemical interactions occurring at the buried sliding interface, which are of key importance for the improvement of the lubrication performance. Yet, these tribochemical processes are very difficult to monitor in real time. Ab initio molecular dynamics simulations are the ideal tool to shed light on such a complicated reactivity. In this work, we perform ab initio simulations, both in static and tribological conditions, to understand the effect of surface oxidation on the tribochemical reactivity of MoDTC, and we find that when the surfaces are covered by oxygen, the first dissociative steps of the additives are significantly hindered. Our preliminary tribological tests on oxidized steel discs support these results. Bare metallic surfaces are necessary for a stable adsorption of the additives, their quick decomposition, and the formation of a durable MoS2 tribolayer. This work demonstrates the importance of the catalytic role of the substrate and confirms the full capability of the computational protocol in the pursuit of materials and compounds more efficient in reducing friction. Graphical abstract: Image 1 Highlights: Oxidation of the steel discs limits the lubricating performance of MoDTC additives. No catalytic effect of the metallic substrate because of poor adsorption of MoDTC. Activation of MoDTC occurs only after removal of the oxide layer.