Molecular Simulations of Kinetic-Friction Modification in Nanoscale Fluid Layers

Farrow, Matthew R.; Chremos, Alexandros; Camp, Philip J.; Harris, Steven G.; Watts, Raymond F.

doi:10.1007/s11249-011-9777-7

Cited by 21 publications

(32 citation statements)

References 38 publications

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“…S8 and is consistent with other Langevin dynamics simulations, which found an approximately linear relationship between the kinetic-friction coefficient of oil fluid layers contained between parallel walls, and sliding velocity at the relatively low velocities examined in this study. 48 These previous kinetic-friction coefficient results were empirically determined but consistent with theory, experiments, and other simulations. 48 Additionally, we find an approximately linear relationship between dynamic con- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 in circular fits near 180 • .…”

Section: Resultssupporting

confidence: 81%

“…48 These previous kinetic-friction coefficient results were empirically determined but consistent with theory, experiments, and other simulations. 48 Additionally, we find an approximately linear relationship between dynamic con- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 in circular fits near 180 • .…”

Section: Resultssupporting

confidence: 81%

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Identifying Differences and Similarities in Static and Dynamic Contact Angles between Nanoscale and Microscale Textured Surfaces Using Molecular Dynamics Simulations

Slovin

Shirts

2015

Langmuir

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We quantify some of the effects of patterned nanoscale surface texture on static contact angles, dynamic contact angles, and dynamic contact angle hysteresis using molecular dynamics simulations of a moving Lennard-Jones droplet in contact with a solid surface. We observe static contact angles that change with the introduction of surface texture in a manner consistent with theoretical and experimental expectations. However, we find that the introduction of nanoscale surface texture at the length scale of 5-10 times the fluid particle size does not affect dynamic contact angle hysteresis even though it changes both the advancing and receding contact angles significantly. This result differs significantly from microscale experimental results where dynamic contact angle hysteresis decreases with the addition of surface texture due to an increase in the receding contact angle. Instead, we find that molecular-kinetic theory, previously applied only to nonpatterned surfaces, accurately describes dynamic contact angle and dynamic contact angle hysteresis behavior as a function of terminal fluid velocity. Therefore, at length scales of tens of nanometers, the kinetic phenomena such as contact line pinning observed at larger scales become insignificant in comparison to the effects of molecular fluctuations for moving droplets, even though the static properties are essentially scale-invariant. These findings may have implications for the design of highly hierarchical structures with particular wetting properties. We also find that quantitatively determining the trends observed in this article requires the careful selection of system and analysis parameters in order to achieve sufficient accuracy and precision in calculated contact angles. Therefore, we provide a detailed description of our two-surface, circular-fit approach to calculating static and dynamic contact angles on surfaces with nanoscale texturing.

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Section: Resultssupporting

confidence: 81%

Section: Resultssupporting

confidence: 81%

Identifying Differences and Similarities in Static and Dynamic Contact Angles between Nanoscale and Microscale Textured Surfaces Using Molecular Dynamics Simulations

Slovin

Shirts

2015

Langmuir

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“…The mechanism of non-Darcian flow behavior was attributed to water-clay interaction by Low (1961). This is further confirmed by a number of studies on nanoscale fluid transport based on MD simulations (e.g., Chen et al, 2008;Ma et al, 2010;Farrow et al, 2011). They generally show that water properties and flow processes at that scale could be significantly different from those in course materials.…”

Section: Correlation Between Permeability and Threshold Gradientsupporting

confidence: 55%

On the relationship between water flux and hydraulic gradient for unsaturated and saturated clay

Liu

Birkhölzer

2012

Journal of Hydrology

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TitleOn the relationship between water-flux and hydraulic gradient for unsaturated and saturated clay AbstractExperimental results indicate that traditional form of Darcy's law is not adequate for describing water flow processes in clay media because the observed relationship between water flux and hydraulic gradient can be highly non-linear. To capture this non-Darcian flow behavior, we proposed a new relationship between water flux and hydraulic gradient by generalizing the currently existing relationships. The new relationship is shown to be consistent with experimental observations for both saturated and unsaturated conditions.In this paper, we also developed an empirical relationship between permeability and threshold hydraulic gradient, an important measure of non-Darcian behavior. The latter relationship is practically useful because it can reduce the number of parameters whose values need to be determined from experiment data in order to model non-Darcian behavior. However, how to incorporate impacts of temperature and electrolyte concentrations into the proposed relationships needs further research.3

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“…It is commonly used to simulate large polymers, where monomers or even a combination of monomers can be represented as a single CG bead. CG-MD has not been extensively applied in tribology; however, it has been used to study friction in polymer brushes [304,305], model friction modifier additives [306] and ionic liquids [68]. The use of CG-MD is likely to remain rare in tribology, since the importance of atomistic detail has been highlighted in accurately reproducing the viscous behaviour of lubricants and additives [10].…”

Section: Linking MD To Larger Scalesmentioning

confidence: 99%

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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Molecular Simulations of Kinetic-Friction Modification in Nanoscale Fluid Layers

Cited by 21 publications

References 38 publications

Identifying Differences and Similarities in Static and Dynamic Contact Angles between Nanoscale and Microscale Textured Surfaces Using Molecular Dynamics Simulations

Identifying Differences and Similarities in Static and Dynamic Contact Angles between Nanoscale and Microscale Textured Surfaces Using Molecular Dynamics Simulations

On the relationship between water flux and hydraulic gradient for unsaturated and saturated clay

Advances in nonequilibrium molecular dynamics simulations of lubricants and additives

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