Molecular Tribometry of Ultrathin Liquid Films

Alsten, John Van; Granick, Steve

doi:10.1103/physrevlett.61.2570

Cited by 396 publications

(233 citation statements)

References 11 publications

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“…2) Friction | https://mc03.manuscriptcentral.com/friction at surface separations equivalent to fewer than nine molecular layers. These simulations support experiments which showed an abrupt transition from liquid-like to solid-like behaviour upon increasing confinement [143,144], rather than a more gradual transition to a glassy state (i.e., vitrification) [142,148]. It is noteworthy that most evidence for vitrification originated from SFA experiments which were later shown to be contaminated with platinum nanoparticles [149], which could go some way to explaining differences between experiments.…”

Section: Density and Viscosity Inhomogeneitysupporting

confidence: 60%

“…A more in-depth discussion of the discrepancies between different experimental techniques and MD simulations of various levels of complexity was given in 2010 by Cummings et al [150]. It has also been shown through experiments [148] and NEMD simulations [145] that elevated pressure can induce such transitions, as well as the associated increase in  eff , in thicker films.…”

Section: Density and Viscosity Inhomogeneitymentioning

confidence: 99%

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Advances in nonequilibrium molecular dynamics simulations of lubricants and additives

2018

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Nonequilibrium molecular dynamics (NEMD) simulations have provided unique insights into the nanoscale behaviour of lubricants under shear. This review discusses the early history of NEMD and its progression from a tool to corroborate theories of the liquid state, to an instrument that can directly evaluate important fluid properties, towards a potential design tool in tribology. The key methodological advances which have allowed this evolution are also highlighted. This is followed by a summary of bulk and confined NEMD simulations of liquid lubricants and lubricant additives, as they have progressed from simple atomic fluids to ever more complex, realistic molecules. The future outlook of NEMD in tribology, including the inclusion of chemical reactivity for additives, and coupling to continuum methods for large systems, is also briefly discussed.

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Section: Density and Viscosity Inhomogeneitysupporting

confidence: 60%

Section: Density and Viscosity Inhomogeneitymentioning

confidence: 99%

Advances in nonequilibrium molecular dynamics simulations of lubricants and additives

2018

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“…The investigations of film thickness, interaction forces, and thin-film shear rheology were performed using a surface forces apparatus (SFA) built in our laboratory, modeled after the "Mark II" SFA 49 and equipped with a device for oscillatory lateral shear. 3,50,51 All experiments were performed at 25°C. The surfaces used were thin sheets of muscovite mica, which were silvered on one side and glued with the silvered side down onto fused silica disks with a half- cylindrical surface.…”

Section: Methodsmentioning

confidence: 99%

Tribology of Confined Fomblin-Z Perfluoropolyalkyl Ethers: Role of Chain-End Chemical Functionality

Ruths

Granick

1999

J. Phys. Chem. B

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Strong dependence of the tribological response upon the nature of the polar end groups of perfluorinated linear chains was observed for Fomblin-Z perfluoropolyalkyl ethers of similar length and composition but terminated by a different polar group at both chain ends. The number-average molecular weight of the polymers was M n ≈ 2000 g mol -1 and the chain-end functionality was either carboxylic acid, hydroxyl, piperonyl, or the p-phenoxyanilinium salt of a carboxylic acid. The method of investigation was a surface forces apparatus modified for dynamic oscillatory shear at variable frequency and effective shear rate. Differences were observed as concerns not only the shear forces but also the minimum thickness to which the films could be compressed under a given normal load and the adhesion measured on separation of the surfaces after prior compression. The shear forces were studied at normal pressures of 1 and 3 MPa, both in the linear viscoelastic regime and at high shear amplitudes corresponding to shear rates of 10 -2 -10 5 s -1 . The carboxylic acid terminated polymer displayed solidlike responses to shear, possibly reflecting dimerization owing to hydrogen bonding. This contrasted with the more fluidlike shear rheology of the hydroxyl-and piperonyl-terminated polymers, in which the association from hydrogen bonding and polar interactions is believed to be weaker and result in a different structure. The sample comprised of the p-phenoxyanilinium salt of a carboxylic acid could not be compressed to less than an exceptionally large film thickness, around 100 Å, and did not appear to solidify at the pressures studied. This study suggests that not only the affinity of the functionalized chain ends to a solid surface but also the self-association of polar end groups in the nonpolar environment of fluorinated chains influences the lubricating performance of these films.

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“…An increase of the viscosity can be characterized by the position of the plane of shear. Simple liquids often show a shear plane which is typically three to six molecular diameters away from the solid-liquid interface [78,994,[1004][1005][1006].…”

Section: Introductionmentioning

confidence: 99%

Force measurements with the atomic force microscope: Technique, interpretation and applications

Butt

Cappella

Kappl

2005

Surface Science Reports

3,218

2,949

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Molecular Tribometry of Ultrathin Liquid Films

Cited by 396 publications

References 11 publications

Advances in nonequilibrium molecular dynamics simulations of lubricants and additives

Advances in nonequilibrium molecular dynamics simulations of lubricants and additives

Tribology of Confined Fomblin-Z Perfluoropolyalkyl Ethers: Role of Chain-End Chemical Functionality

Force measurements with the atomic force microscope: Technique, interpretation and applications

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