Thickness and drainage of perfluoropolyethers under compression

Xu, Lei; Ogletree, D. Frank; Salmerón, Miquel; Tang, Huan; Ma, Xiading; Gui, Jing

doi:10.1063/1.1375136

Cited by 10 publications

(7 citation statements)

References 25 publications

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“…Many of these liquids, including Demnum-S20, exhibit solidlike behavior during shearing ͑a finite yield stress is needed to initiate sliding͒. 11,[13][14][15] In our blow-off experiments with Demnum-S20, neither enhancement of viscosity nor solidification is observed, which is consistent with our previous results 3 using Fomblin-Z. We attribute the viscosity increase and yield stress observed in SFA experiments to confinement of molecules between the two solid surfaces with an applied normal stress.…”

Section: Surface-force-apparatus "Sfa…supporting

confidence: 93%

“…This decrease is presumably caused by both of ends of the Fomblin-Zdol chain being attracted to the substrate, instead of just one end as for Demnum-SA, reducing the degree that the polymer chain extends from the substrate. Xu et al 11 argue that a linear polymer attached at only one end should extend on average & times further away from the substrate than a polymer attached at both ends.…”

Section: Figures 2 and 3 Show Examples Of The Thickness Profilesmentioning

confidence: 99%

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Air shear driven flow of thin perfluoropolyether polymer films

Scarpulla

Mate

Carter

2003

The Journal of Chemical Physics

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We have studied the wind driven movement of thin perfluoropolyether (PFPE) polymer films on silicon wafers and CNx overcoats using the blow-off technique. The ease with which a liquid polymer film moves across a surface when sheared is described by a shear mobility χS, which can be interpreted both in terms of continuum flow and in terms of wind driven diffusion. Generally, we find that the movement of PFPE films can be described as a flow process with an effective viscosity, even when the film thickness is smaller than the polymer’s diameter of gyration. Only in the special case of sparse coverage of a polymer with neutral end groups is the motion better described by a wind driven diffusion process. The addition of alcohol end groups to the PFPE polymer chain results in strong interactions with the substrate, creating a restricted layer having an effective viscosity an order of magnitude larger than the mobile layer that sits on top of the restricted layer.

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Section: Surface-force-apparatus "Sfa…supporting

confidence: 93%

Section: Figures 2 and 3 Show Examples Of The Thickness Profilesmentioning

confidence: 99%

Air shear driven flow of thin perfluoropolyether polymer films

Scarpulla

Mate

Carter

2003

The Journal of Chemical Physics

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“…Therefore, the results shown in Figs the molecule is non-polar and is physically adsorbed onto the solid surface only by van der Waals force [16,17]. Moreover, it was reported that the liquid lubricant was completely squeezed out by the drainage experiment using an SFA [18]. Therefore, the error due to insufficient removal of the liquid is regarded as being small.…”

Section: Resultsmentioning

confidence: 87%

Simultaneously Measuring Lateral and Vertical Forces with Accurate Gap Control for Clarifying Lubrication Phenomena at Nanometer Gap

et al. 2009

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A novel method for simultaneous measurement of vertical and lateral forces with high sensitivity and accurate gap control is presented. It combines a doubleended tuning fork resonator for vertical force measurement with an optical fiber probe for lateral force measurement. High force sensitivity of several tens of nano Newons with accurate gap control of less than 1 nm was successfully attained. Simultaneous measurement using this novel method revealed that viscoelasticity increased with decrease of the sliding gap. Moreover, the method first revealed that the lubricant pressure generated by the wedge effect can increase due to the confinement at small gaps, even if the lubricant pressure is so low that the viscosity rise due to the pressure is much small. This method is expected to be useful for clarifying the lubrication phenomena at nanometer sliding gaps, which are not yet fully understood due to the difficulty of measurement.

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“…The responsible friction mechanism of the FAE film is not analogous to that of the commonly used fluorinated liquid lubricants such as PFPEs (which behave as a typical liquid lubricant) 28,29 but rather close to that of fluorocarbon (FC) monolayers. The FAE film consists of two adsorbed layers on mica substrates which act as fluorinated coatings, and no "mobile" middle layers exist.…”

Section: Discussionmentioning

confidence: 95%

Nanotribology of Ethers: Effects of Molecular Asymmetry and Fluoroalkyl Chains

Yamada

2005

Langmuir

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The tribological properties of the molecularly thin films of asymmetric ether (1,3-dimethylbutyl octyl ether, AE) and fluorinated asymmetric ether (1H,1H,2H,2H-perfluorooctyl-1,3-dimethylbutyl ether, FAE) were investigated. Friction forces and dynamic thicknesses (thicknesses during sliding) were simultaneously measured using the surface forces apparatus, and the effects of molecular asymmetry and fluoroalkyl chains on the friction properties are analyzed. The friction forces (both kinetic and static) and dynamic thicknesses are larger for the AE film than for the FAE film. The two ethers exhibit stick-slip friction at low sliding velocity, but the stick-slip patterns are different. For the AE film, one stick-slip cycle consists of two or more spikes; a large spike is followed by one or more small spike(s) in the cycle. On the other hand, regular stick-slip spikes are observed for the FAE film. The results suggest that the responsible friction mechanisms are completely different between the two ether films. The asymmetric shape of the AE molecule results in a variety of shear-ordered liquid structures in confinement, and the friction (stick-slip) behavior follows the "phase-transition model". In contrast, the FAE molecule is rigid, and the shape of the molecule is rather close to a symmetric cylinder, which leads to a well-ordered two-layer film in confinement. The each molecular layer is strongly adsorbed on adjacent mica substrate and behaves as a fluorinated coating. The friction is governed by the molecular scale "bumpiness" of the fluoroalkyl chains lying on mica surfaces and basically follows the "cobblestone model". The advantage of the thin FAE film as a practical lubricant is also discussed.

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Thickness and drainage of perfluoropolyethers under compression

Abstract: Compressibility and strength of nanocrystalline tungsten boride under compression to 60GPa

Cited by 10 publications

References 25 publications

Air shear driven flow of thin perfluoropolyether polymer films

Air shear driven flow of thin perfluoropolyether polymer films

Simultaneously Measuring Lateral and Vertical Forces with Accurate Gap Control for Clarifying Lubrication Phenomena at Nanometer Gap

Nanotribology of Ethers: Effects of Molecular Asymmetry and Fluoroalkyl Chains

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