Heat-, Load-, and Shear-Driven Reactions of Di-<i>tert</i>-butyl Disulfide on Fe(100)

Mohammadtabar, Karen; Eder, Stefan J.; Dörr, Nicole; Martini, Ashlie

doi:10.1021/acs.jpcc.9b05068

Cited by 18 publications

(24 citation statements)

References 37 publications

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“…Simulations of sliding across a range of temperatures showed that shear accelerates the reaction and increases the reaction yield [83] The reaction yield was quantified by the rate-limiting step, and the simulations demonstrated that the energy barrier was lowered by shear force acting along the reaction coordinate for the rate limiting step of the reaction. Next, the reaction yield at each temperature was fit to the Bell model [25], Equation 1, rewritten as [83]:…”

Section: Reactions Between Lubricants and Surfacesmentioning

confidence: 96%

“…The reaction pathway was identified as dissociation of the di-tert-butyl disulfide (S-S bond breaking), chemisorption of tert-butyl sulfide (Fe-S bond formation), and then, tert-butyl radical release (S-C bond breaking), as illustrated in Figure 5a-c, where the radical release was found to be the rate-limiting step [51]. Simulations of sliding across a range of temperatures showed that shear accelerates the reaction and increases the reaction yield [83] The reaction yield was quantified by the rate-limiting step, and the simulations demonstrated that the energy barrier was lowered by shear force acting along the reaction coordinate for the rate limiting step of the reaction. Next, the reaction yield at each temperature was fit to the Bell model [25], Equation 1, rewritten as [83]:…”

Section: Reactions Between Lubricants and Surfacesmentioning

confidence: 98%

“…Many practical applications of tribology involve ferrous surfaces and recent studies with di-tert butyl disulfide, an extreme pressure additive, and Fe(100) surfaces were performed using ReaxFF [51,83]. The reaction pathway was identified as dissociation of the di-tert-butyl disulfide (S-S bond breaking), chemisorption of tert-butyl sulfide (Fe-S bond formation), and then, tert-butyl radical release (S-C bond breaking), as illustrated in Figure 5a-c, where the radical release was found to be the rate-limiting step [51].…”

Section: Reactions Between Lubricants and Surfacesmentioning

confidence: 99%

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Tribochemistry: A Review of Reactive Molecular Dynamics Simulations

2020

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Tribochemistry, the study of chemical reactions in tribological interfaces, plays a critical role in determining friction and wear behavior. One method researchers have used to explore tribochemistry is “reactive” molecular dynamics simulation based on empirical models that capture the formation and breaking of chemical bonds. This review summarizes studies that have been performed using reactive molecular dynamics simulations of chemical reactions in sliding contacts. Topics include shear-driven reactions between and within solid surfaces, between solid surfaces and lubricating fluids, and within lubricating fluids. The review concludes with a perspective on the contributions of reactive molecular dynamics simulations to the current understanding of tribochemistry, as well as opportunities for this approach going forward.

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Section: Reactions Between Lubricants and Surfacesmentioning

confidence: 96%

Section: Reactions Between Lubricants and Surfacesmentioning

confidence: 98%

Section: Reactions Between Lubricants and Surfacesmentioning

confidence: 99%

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Tribochemistry: A Review of Reactive Molecular Dynamics Simulations

2020

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“…28 Indeed, NEMD simulations have recently been performed for a wide range of other systems using ReaxFF. [99][100][101] It will also be useful to validate the results of the ReaxFF NEMD simulations against AIMD simulations. For example,…”

Section: Simulationsmentioning

confidence: 99%

Substituent Effects on the Thermal Decomposition of Phosphate Esters on Ferrous Surfaces

et al. 2020

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Phosphate esters have a wide range of industrial applications, for example in tribology where they are used as vapour phase lubricants and antiwear additives. An atomic-level understanding of phosphate ester tribofilm formation mechanisms is required to improve their tribological performance. A process of particular interest is the thermal decomposition of phosphate esters on steel surfaces, since this initiates polyphosphate film formation. In this study, reactive force field (ReaxFF) molecular dynamics (MD) simulations are used to study the thermal decomposition of phosphate esters with different substituents on several ferrous surfaces. The ReaxFF parameterisation was validated for a representative system using density functional theory (DFT) calculations. During the MD simulations on Fe3O4(001) and α-Fe(110), chemisorption interactions between the phosphate esters and the surfaces occur even at room temperature, and the number of molecule-surface bonds increases as the temperature increases from 300 to 1000 K. Conversely, on hydroxylated, amorphous Fe3O4, most of the molecules are physisorbed and some desorption occurs at high temperature. Thermal decomposition rates were much higher on Fe3O4(001) and particularly α-Fe(110) compared to hydroxylated, amorphous Fe3O4. This suggests that water passivates ferrous surfaces and inhibits phosphate ester chemisorption, decomposition, and ultimately polyphosphate film formation. For the alkyl phosphates, thermal decomposition proceeds mainly through CO and C-H cleavage on Fe3O4(001). Aryl phosphates show much higher thermal stability, and decomposition on Fe3O4(001) only occurs through P-O and C-H cleavage, which require very high temperature. The onset temperature for CO cleavage on Fe3O4(001) increases as: tertiary alkyl < secondary alkyl < primary linear alkyl ≈ primary branched alkyl < aryl. This order is consistent with experimental observations for the thermal stability of antiwear additives with similar substituents. The simulation results clarify a range of surface and substituent effects on the thermal decomposition of phosphate esters on steel that should be helpful for the design of new molecules with improved tribological performance.

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“…28 For example, NEMD simulations have recently been used to study the tribopolymerization of aldehydes between alumina surfaces, 29 phosphoric acid, 30,31 allyl alcohols, 32 and terpenes 33 between sliding silica surfaces, and cyclopropane carboxylic acid between iron oxide surfaces. 34 They have also been used to study the mechanochemical decomposition of alkyl sulfides between sliding iron surfaces 35 and perfluoropolyethers (PFPEs) between DLC surfaces, 36 the vapour phase lubrication of trialkylphosphates 37 and trialkylphosphites 38,39 between iron surfaces, and the ultralow friction of organic friction modifier additives between DLC surfaces. 40 Most of these NEMD simulations employed many-body empirical force fields, [30][31][32][33][34][35][36] while others use first principles methods, 29,[37][38][39] or sometimes a combination of both of these techniques.…”

Section: Introductionmentioning

confidence: 99%

Mechanochemistry of Phosphate Esters Confined between Sliding Iron Surfaces

Latorre

Remias

Moore

et al. 2021

Preprint

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Small changes to the molecular structure of lubricant additives affect their adsorption and dissociation behaviour at the nanoscale, as well as their friction and wear performance at the macroscale. Here, we show using nonequilibrium molecular dynamics simulations with a reactive force field that secondary trialkylphosphates dissociate much faster than primary trialkylphosphates between sliding iron surfaces. For both molecules, dissociative chemisorption proceeds through cleavage of the carbon − oxygen bond. The rate increases exponentially with temperature and stress, which is indicative of a stress-augmented thermally activated process. Both molecules show similar activation energy and activation volume. The much higher reactivity of secondary trialkylphosphates is driven mostly by the pre-exponential factor, which is almost an order of magnitude larger than for primary trialkylphosphates. These observations and the associated kinetic parameters are consistent with recent macroscale tribometer experiments of the antiwear additive zinc dialkyldithiophosphate. This study represents a crucial step towards the virtual screening of lubricant additives with different substituents for optimal tribological performance.

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Heat-, Load-, and Shear-Driven Reactions of Di-tert-butyl Disulfide on Fe(100)

Cited by 18 publications

References 37 publications

Tribochemistry: A Review of Reactive Molecular Dynamics Simulations

Tribochemistry: A Review of Reactive Molecular Dynamics Simulations

Substituent Effects on the Thermal Decomposition of Phosphate Esters on Ferrous Surfaces

Mechanochemistry of Phosphate Esters Confined between Sliding Iron Surfaces

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