Experimental and Ab Initio Characterization of Mononuclear Molybdenum Dithiocarbamates in Lubricant Mixtures

Abstract

Molybdenum dithiocarbamates (MoDTCs) are a class of lubricant additives widely employed in automotives. Most of the studies concerning MoDTC take into account the dimeric structures because of their industrial relevance, with the mononuclear compounds usually neglected, because isolating and characterizing subgroups of MoDTC molecules are generally difficult. However, the byproducts of the synthesis of MoDTC can impact the friction reduction performance at metallic interfaces, and the effect of mononuclear MoDTC (mMoDTC) compounds in the lubrication has not been considered yet in the literature. In this study, we consider for the first time the impurities of MoDTC consisting of mononuclear compounds and combine experimental and computational techniques to elucidate the interaction of these impurities with binuclear MoDTC in commercial formulations. We present a preliminary strategy to separate a commercial MoDTC product in chemically different fractions. These fractions present different tribological behaviors depending on the relative amount of mononuclear and binuclear complexes. The calculations indicate that the dissociation mechanism of mMoDTC is similar to the one observed for the dimeric structures. However, the different chemical properties of mMoDTC impact the kinetics for the formation of the beneficial molybdenum disulfide (MoS 2 ) layers, as shown by the tribological experiments. These results help to understand the functionality of MoDTC lubricant additives, providing new insights into the complex synergy between the different chemical structures.

Importance of Short-Range Order in Governing Thin Film Morphology and Electronic Properties of Polymeric Organic Semiconductors

“…In addition, a lower frequency signal at 2.3 MHz with a small ridge is expected to originate from the double quanta of 33 S (natural isotopic abundance = 0.76%). Such a feature has already been detected in S-rich molecules . This analysis suggests that stronger hyperfine interactions are observed with the carbon atoms via a dipolar mechanism, and relatively weak interactions exist with S and H sites.…”

“…Such a feature has already been detected in S-rich molecules. 72 This analysis suggests that stronger hyperfine interactions are observed with the carbon atoms via a dipolar mechanism, and relatively weak interactions exist with S and H sites. Taken together, the presence of paramagnetic and diamagnetic species and locally ordered and disordered species manifest as heterogeneities in the thin film morphology.…”

Modeling phosphorene and $$\hbox {MoS}_{2}$$ interacting with iron: lubricating effects compared to graphene

“…To understand the connection between adhesive friction and interfacial electronic properties, we evaluate the charge redistribution occurring in the interfacial region, as described in Ref. [19] and later in the text. The charge redistribution is normalized by the average number of electrons per atom to compare different systems.…”

“…Here, we use first-principles calculations to explore the capability of phosphorene to chemisorb on iron and reduce its adhesion and friction. A similar analysis is performed for MoS 2 , a well-known solid lubricant, which can also lubricate steel as a product of tribochemical reactions involving lubricant additives, such as molybdenum dithiocarbamates [17][18][19].…”

2D KBr/Graphene Heterostructures—Influence on Work Function and Friction

“…The plane-wave expansion of the electronic wave function (charge density) was limited to a kinetic energy cutoff of 30 Rydberg ( 240 Ry), since the pseudopotentials used in this work were ultrasoft. We did not take into account dispersion forces, as we did in our previous works [ 27 , 28 , 29 , 30 ], because these corrections often overestimate the bond energies involving metallic substrates [ 31 , 32 ]. A Gaussian smearing of Ry was used to better describe the electronic occupations around the Fermi level.…”