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Waltman, R. J.; Pocker, D. J.; Tyndall, George W.

doi:10.1023/a:1019127910531

Cited by 68 publications

(53 citation statements)

References 12 publications

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“…We also note that experiments 47 on higher molecular weight hydroxyl-and piperonyl-terminated Fomblin-Z revealed that, for these polymers, larger film thicknesses were obtained for higher molecular weights at a given normal pressure. The absence of an oscillatory interaction force as a function of surface separation (Figure 1) suggests that a semiordered layering (as in thin films of linear alkanes 55 or poly-(dimethylsiloxane) 68 confined between atomically smooth surfaces) was hindered in our end-functionalized systems, even though it has been demonstrated that the perfluorinated backbone of DIAC, 21 DOL, 21,39,40 and AM2001 30 adopts an orientation parallel to polar surfaces. The influence of localization of end groups to the solid surface and of end group-end group interactions on the structure of the confined film will be discussed further below.…”

Section: Discussionmentioning

confidence: 91%

“…It is, however, unlikely that a polar group like carboxylic acid 21,42 would fail to physisorb to a polar surface as, for example, the hydroxyl groups in DOL, [19][20][21][22][23][24][25][26]28,29,[32][33][34][35][38][39][40]73 the piperonyl groups in AM2001, 30,31 or the p-phenoxyanilinium group 41 are expected to do.…”

Section: Discussionmentioning

confidence: 99%

“…Several end-functionalized Fomblin-Z polymers are widely used in commercial magnetic storage devices. [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][38][39][40] This family of chain polymers therefore provides a useful system in which to examine the influence of chain-end functionality.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Discussionmentioning

confidence: 91%

Section: Discussionmentioning

confidence: 99%

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

Ruths

Granick

1999

J. Phys. Chem. B

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“…The dispersive (indicated with superscript d) and polar (indicated with superscript p) surface energy components are c 1 d =27.6 mN/m, c 1 p =0 mN/m for hexadecane (nonpolar liquid), and c 1 d =21.8 mN/m, c 1 p =51.0 mN/m for water (polar liquid), where the subscript l refers to liquid. Using the following equation, the dispersive (c s d ) and polar (c s p ) surface energy components, respectively, of the lubricated disk surface were determined from the contact angles h made with the surface by hexadecane and water [12,13].…”

Section: Surface Energymentioning

confidence: 99%

Effect of Ultraviolet Irradiation on the Interactions between Perfluoropolyether Lubricant and Magnetic Disk Surfaces

et al. 2005

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To tailor the characteristics of molecularly thin lubricant films, magnetic disk surfaces coated with nanometer-thick perfluoropolyether AM3001 lubricant films were irradiated with 184.9 and 253.7 nm ultraviolet (UV) rays. We elucidated the effect of UV irradiation on the interactions between the lubricant and the magnetic disk surface via surface energy, bonded lubricant thickness and lubricant spreading measurements for films with and without UV irradiation. We found that UV irradiation decreased the dispersive and polar surface energies of the lubricant films by 20 and 80%, respectively; increased bonded lubricant thickness; and decelerated lubricant spreading. These results indicated that dispersion and polar interactions between lubricant molecules and the magnetic disk surface were strengthened by UV irradiation.

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“…Mechanical spacing between the head slider and the disk has steadily decreased, so that now the flying height is approximately less than about 10 nm above the disk surface. Perfluoropolyether (PFPE) derivatives have been widely used for the lubricant layers of magnetic recording disks because of their good lubricity, low-surface energy, high-thermal stability and low-vapor pressure [1][2][3]. The film thickness of lubricant layers on disk surface is $1 nm.…”

Section: Introductionmentioning

confidence: 99%

Direct observation of PFPE lubricant molecules by cryogenic AFM under ultra-high vacuum

et al. 2006

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Surface lubrication is one of the essential technologies in modern magnetic disk systems and improvement of the surface lubrication is very important in the development of next generation systems. In this study, we used AFM for the direct observation of perfluoropolyether (PFPE) lubricant molecules on atomically flat surfaces. We used a cryogenic non-contact AFM to observe the molecules in a frozen state of micro-Brownian motion of PFPE segments, because the glass transition temperature of PFPE is very low. To avoid freezing a trace amount of water vapor on the sample surface at liquid nitrogen temperatures, the AFM observation was performed under ultra-high vacuum. We observed that on a gold surface the size of the molecules increases with repeated AFM scans. This is because the mechanical stimulus causes the fusion of PFPE lubricant molecules to form reversed micelles at the non-polar surface. At a hydrophilic silicon wafer surface, however, we succeeded in observing single lubricant molecules. This is because almost all PFPE lubricant molecules are fixed to the hydrophilic solid surface by polar-polar bond formation and they cannot move around on the surface and thus they cannot fuse to each other. As formation of the reversed micelle structure is a rather general phenomenon in the PFPE lubricant thin layer at non-polar surfaces, we also will discuss briefly the expected molecular structures of PFPE lubricants at the surface of the carbon overcoat of magnetic disks.

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Untitled

Cited by 68 publications

References 12 publications

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

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

Effect of Ultraviolet Irradiation on the Interactions between Perfluoropolyether Lubricant and Magnetic Disk Surfaces

Direct observation of PFPE lubricant molecules by cryogenic AFM under ultra-high vacuum

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