scholarly journals Mechanochemistry of Phosphate Esters Confined between Sliding Iron Surfaces

2021 ◽  
Author(s):  
Carlos Ayestarán Latorre ◽  
Joseph Remias ◽  
Joshua Moore ◽  
Hugh Spikes ◽  
Daniele Dini ◽  
...  
Keyword(s):  
Lubricant Additives ◽  
Nonequilibrium Molecular Dynamics ◽  
Dissociative Chemisorption ◽  
Wear Performance ◽  
Exponential Factor ◽  
Thermally Activated ◽  
Order Of Magnitude ◽  
Dynamics Simulations ◽  
Adsorption And Dissociation ◽  
Oxygen Bond

Abstract 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.

scholarly journals Mechanochemistry of phosphate esters confined between sliding iron surfaces

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Carlos Ayestarán Latorre ◽  
Joseph E. Remias ◽  
Joshua D. Moore ◽  
Hugh A. Spikes ◽  
Daniele Dini ◽  
...  
Keyword(s):  
Friction And Wear ◽  
Dissociation Rate ◽  
Lubricant Additives ◽  
Phosphate Esters ◽  
Nonequilibrium Molecular Dynamics ◽  
Zinc Dialkyldithiophosphate ◽  
Dissociative Chemisorption ◽  
Exponential Factor ◽  
Dynamics Simulations ◽  
Adsorption And Dissociation

AbstractThe molecular structure of lubricant additives controls not only their adsorption and dissociation behaviour at the nanoscale, but also their ability to reduce friction and wear at the macroscale. Here, we show using nonequilibrium molecular dynamics simulations with a reactive force field that tri(s-butyl)phosphate dissociates much faster than tri(n-butyl)phosphate when heated and compressed between sliding iron surfaces. For both molecules, dissociative chemisorption proceeds through cleavage of carbon−oxygen bonds. The dissociation rate increases exponentially with temperature and stress. When the rate−temperature−stress data are fitted with the Bell model, both molecules have similar activation energies and activation volumes and the higher reactivity of tri(s-butyl)phosphate is due to a larger pre-exponential factor. These observations are consistent with experiments using the antiwear additive zinc dialkyldithiophosphate. This study represents a crucial step towards the virtual screening of lubricant additives with different substituents to optimise tribological performance.

Controlling Thermal Conductivity of Alloys via Atomic Ordering

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
John C. Duda ◽  
Timothy S. English ◽  
Donald A. Jordan ◽  
Pamela M. Norris ◽  
William A. Soffa
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Nonequilibrium Molecular Dynamics ◽  
Melt Temperature ◽  
Lennard Jones ◽  
Thermodynamic Conditions ◽  
Order Of Magnitude ◽  
Fixed Composition ◽  
Dynamics Simulations

Many random substitutional solid solutions (alloys) will display a tendency to atomically order given the appropriate kinetic and thermodynamic conditions. Such order–disorder transitions will result in major crystallographic reconfigurations, where the atomic basis, symmetry, and periodicity of the alloy change dramatically. Consequently, phonon behavior in these alloys will vary greatly depending on the type and degree of ordering achieved. To investigate these phenomena, the role of the order–disorder transition on phononic transport properties of Lennard–Jones type binary alloys is explored via nonequilibrium molecular dynamics simulations. Particular attention is paid to regimes in which the alloy is only partially ordered. It is shown that by varying the degree of ordering, the thermal conductivity of a binary alloy of fixed composition can be tuned across an order of magnitude at 10% of the melt temperature, and by a factor of three at 40% of the melt temperature.

scholarly journals Fluctuation Relations for Dissipative Systems in Constant External Magnetic Field: Theory and Molecular Dynamics Simulations

Entropy ◽  
2021 ◽  
Vol 23 (2) ◽  
pp. 146
Author(s):  
Alessandro Coretti ◽  
Lamberto Rondoni ◽  
Sara Bonella
Keyword(s):  
Magnetic Field ◽  
Molecular Dynamics ◽  
External Magnetic Field ◽  
Molecular Dynamics Simulations ◽  
Nonequilibrium Molecular Dynamics ◽  
Dissipative Systems ◽  
Common Belief ◽  
Fluctuation Relations ◽  
Dynamics Simulations ◽  
Constant External Magnetic Field

We illustrate how, contrary to common belief, transient Fluctuation Relations (FRs) for systems in constant external magnetic field hold without the inversion of the field. Building on previous work providing generalized time-reversal symmetries for systems in parallel external magnetic and electric fields, we observe that the standard proof of these important nonequilibrium properties can be fully reinstated in the presence of net dissipation. This generalizes recent results for the FRs in orthogonal fields—an interesting but less commonly investigated geometry—and enables direct comparison with existing literature. We also present for the first time a numerical demonstration of the validity of the transient FRs with nonzero magnetic field via nonequilibrium molecular dynamics simulations of a realistic model of liquid NaCl.

scholarly journals A de novo substitution in BCL11B leads to loss of interaction with transcriptional complexes and craniosynostosis

2019 ◽  
Vol 28 (15) ◽  
pp. 2501-2513 ◽  
Author(s):  
Jacqueline A C Goos ◽  
Walter K Vogel ◽  
Hana Mlcochova ◽  
Christopher J Millard ◽  
Elahe Esfandiari ◽  
...  
Keyword(s):  
De Novo ◽  
Cranial Sutures ◽  
Coronal Suture ◽  
Nurd Complex ◽  
Binding Studies ◽  
Amino Terminal ◽  
Skull Vault ◽  
Order Of Magnitude ◽  
Transcriptional Complexes ◽  
Dynamics Simulations

Abstract Craniosynostosis, the premature ossification of cranial sutures, is a developmental disorder of the skull vault, occurring in approximately 1 in 2250 births. The causes are heterogeneous, with a monogenic basis identified in ~25% of patients. Using whole-genome sequencing, we identified a novel, de novo variant in BCL11B, c.7C>A, encoding an R3S substitution (p.R3S), in a male patient with coronal suture synostosis. BCL11B is a transcription factor that interacts directly with the nucleosome remodelling and deacetylation complex (NuRD) and polycomb-related complex 2 (PRC2) through the invariant proteins RBBP4 and RBBP7. The p.R3S substitution occurs within a conserved amino-terminal motif (RRKQxxP) of BCL11B and reduces interaction with both transcriptional complexes. Equilibrium binding studies and molecular dynamics simulations show that the p.R3S substitution disrupts ionic coordination between BCL11B and the RBBP4–MTA1 complex, a subassembly of the NuRD complex, and increases the conformational flexibility of Arg-4, Lys-5 and Gln-6 of BCL11B. These alterations collectively reduce the affinity of BCL11B p.R3S for the RBBP4–MTA1 complex by nearly an order of magnitude. We generated a mouse model of the BCL11B p.R3S substitution using a CRISPR-Cas9-based approach, and we report herein that these mice exhibit craniosynostosis of the coronal suture, as well as other cranial sutures. This finding provides strong evidence that the BCL11B p.R3S substitution is causally associated with craniosynostosis and confirms an important role for BCL11B in the maintenance of cranial suture patency.

Structure and Conductivity of Iodine-Doped C60 Thin Films

1994 ◽  
Vol 359 ◽  
Author(s):  
Jun Chen ◽  
Haiyan Zhang ◽  
Baoqiong Chen ◽  
Shaoqi Peng ◽  
Ning Ke ◽  
...  
Keyword(s):  
Thin Films ◽  
Electrical Conductivity ◽  
Room Temperature ◽  
Conductivity Measurements ◽  
X Ray Diffraction ◽  
Temperature Conductivity ◽  
Room Temperature Conductivity ◽  
X Ray ◽  
Thermally Activated ◽  
Order Of Magnitude

ABSTRACTWe report here the results of our study on the properties of iodine-doped C60 thin films by IR and optical absorption, X-ray diffraction, and electrical conductivity measurements. The results show that there is no apparent structural change in the iodine-doped samples at room temperature in comparison with that of the undoped films. However, in the electrical conductivity measurements, an increase of more that one order of magnitude in the room temperature conductivity has been observed in the iodine-doped samples. In addition, while the conductivity of the undoped films shows thermally activated temperature dependence, the conductivity of the iodine-doped films was found to be constant over a fairly wide temperature range (from 20°C to 70°C) exhibiting a metallic feature.

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