The Influence of Lubrication and the Solid–Fluid Interaction on Thermodynamic Properties in a Nanoscopic Scratching Process

Stephan, Simon; Dyga, Maximilian; Urbassek, Herbert M.; Hasse, Hans

doi:10.1021/acs.langmuir.9b01033

Cited by 33 publications

(59 citation statements)

References 127 publications

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“…An increase in h compared to the undisturbed region at the leading (pileup) and trailing (debris) edge of the tip is observed at low coverage (Γ = 2-3 nm −2 ). Similar behaviour has previously been observed in indentation NEMD simulations of solid iron 77 and OTS monolayers on a-SiO 2 surfaces. 48 At high coverage (Γ = 5 nm −2 ), there is a small reduction in h (depletion) at the leading edge of the tip.…”

Section: Indentation Depthsupporting

confidence: 87%

Scale-Dependent Friction-Coverage Relations and Non-Local Dissipation in Surfactant Monolayers

Gao¹,

Ewen

Hartkamp³

et al. 2021

Preprint

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<div>Surfactant molecules, known as organic friction modifiers (OFMs), are added to lubricants to reduce friction and wear between sliding surfaces. In macroscale experiments, friction generally decreases as the coverage of OFM molecules on the sliding surfaces increases. However, recent nanoscale experiments with sharp atomic force microscopy (AFM) tips have shown increasing friction. To elucidate the origin of these opposite trends, we use nonequilibrium molecular dynamics (NEMD) simulations and study kinetic friction between OFM monolayers and an indenting nanoscale asperity. For this purpose, we study various coverages of stearamide OFMs on iron oxide surfaces and silica AFM tips with different radii of curvature. For our small tip radii, the friction coefficient and indentation depth both have a non-monotonic dependence on OFM surface coverage, with maxima occurring at intermediate coverage. This suggests that friction is dominated by plowing. We rationalise the non-monotonic relations through a competition of two effects (confinement and packing density) that varying the surface coverage has on the effective stiffness of the OFM monolayers. We also show that kinetic friction is not very sensitive to the sliding velocity in the range studied, indicating that it originates from instabilities. Indeed, while friction predominately originates from the plowing action of the monolayers by the leading edge of the tip, thermal dissipation is mostly localised in molecules towards the trailing edge of the tip.</div>

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Section: Indentation Depthsupporting

confidence: 87%

Scale-Dependent Friction-Coverage Relations and Non-Local Dissipation in Surfactant Monolayers

Gao¹,

Ewen

Hartkamp³

et al. 2021

Preprint

View full text Add to dashboard Cite

show abstract

“…An increase in h compared to the undisturbed region at the leading and trailing edge of the tip is observed at low coverage (Γ = 2-3 nm −2 ). Similar behaviour has previously been observed in indentation NEMD simulations of solid iron 73 and OTS monolayers on a-SiO 2 surfaces. 43 At high coverage (Γ = 5 nm −2 ), there is a small reduction in h (depletion) at the leading edge of the tip.…”

Section: Indentation Depthsupporting

confidence: 87%

Scale-Dependent Friction-Coverage Relations and Non-Local Dissipation in Surfactant Monolayers

Gao¹,

Ewen

Hartkamp³

et al. 2020

Preprint

View full text Add to dashboard Cite

<div>Surfactant molecules, known as organic friction modi?ers (OFMs), are added to lubricants to reduce friction and wear between sliding surfaces. In macroscale experiments, friction generally decreases as the coverage of OFM molecules on the sliding surfaces increases. However, recent nanoscale experiments with sharp atomic force microscopy (AFM) tips have shown increasing friction. To elucidate the origin of these opposite trends, we use nonequilibrium molecular dynamics (NEMD) simulations and study kinetic friction between OFM monolayers and an indenting nanoscale asperity. For this purpose, we study various coverages of stearamide OFMs on iron oxide surfaces and silica AFM tips with different radii of curvature. For our small tip radii, the friction coefficient and indentation depth both have a non-monotonic dependence on OFM surface coverage, with maxima occurring at intermediate coverage. This suggests that friction is dominated by plowing. We rationalise the non-monotonic relations through</div><div>a competition of two effects (confinement and packing density) that varying the surface coverage has on the effective stiffness of the OFM monolayers. We also show</div><div>that kinetic friction is not very sensitive to the sliding velocity in the range studied, indicating that it originates from instabilities. Indeed, while friction predominately</div><div>originates from the plowing action of the monolayers by the leading edge of the tip, thermal dissipation is mostly localised in molecules towards the trailing edge of the tip.</div>

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“…This phenomenon is mainly due to the alignment pattern between the upper and lower walls. Similar jump in the friction force was also observed by Stephan et al [49], in which the simulated tangential force increased as the chip started to form at the beginning of the lateral movement. On the other hand, An and co-authors [50] have successfully proposed a quantitative relationship of the nanoscale friction force and coefficient between liquid and solid based on their atomic force microscopy experimental characterizations.…”

Section: Dry Contactsupporting

confidence: 84%

Study on Lubrication Characteristics of C4-Alkane and Nanoparticle during Boundary Friction by Molecular Dynamics Simulation

Zheng

Deng

et al. 2021

Metals

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Lubricant has been widely applied to reduce wear and friction between the contact surfaces when they are in relative motion. In the current study, a nonequilibrium molecular dynamics (NEMD) simulation was specifically established to conduct a comprehensive investigation on the dynamic contact between two iron surfaces in a boundary friction system considering the mixed C4-alkane and nanoparticles as lubricant. The main research objective was to explore the effects of fluid and nanoparticles addition on the surface contact and friction force. It was found that nanoparticles acted like ball bearings between the contact surfaces, leading to a change of sliding friction mode to rolling friction mode. Under normal loads, plastic deformation occurred at the top surface because nanoparticles were mainly supporting the normal load. By increasing the number of C4-alkane molecules between two contact surfaces, the contact condition has been changed from partial to full lubrication. In addition, an attractive force from the solid–liquid LJ interaction between C4-alkane and surfaces was observed at the early stage of sliding, due to the large space formed by wall surfaces and nanoparticles. The findings in this paper would be beneficial for understanding the frictional behavior of a simple lubricant with or without nanoparticles addition in a small confinement.

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The Influence of Lubrication and the Solid–Fluid Interaction on Thermodynamic Properties in a Nanoscopic Scratching Process

Cited by 33 publications

References 127 publications

Scale-Dependent Friction-Coverage Relations and Non-Local Dissipation in Surfactant Monolayers

Scale-Dependent Friction-Coverage Relations and Non-Local Dissipation in Surfactant Monolayers

Scale-Dependent Friction-Coverage Relations and Non-Local Dissipation in Surfactant Monolayers

Study on Lubrication Characteristics of C4-Alkane and Nanoparticle during Boundary Friction by Molecular Dynamics Simulation

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