Micro/nanoscale studies of boundary layers of liquid lubricants for magnetic disks

Koinkar, Vilas N.; Bhushan, Bharat

doi:10.1063/1.362361

Cited by 93 publications

(41 citation statements)

References 4 publications

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“…The DOL and AM2001 appear to have more favorable lubricating properties than unfunctionalized Fomblin-Z, as has been found previously in different types of sliding experiments. 19,[23][24][25]28,29,38 On a magnetic tape covered with lubricant and SiO 2 particles, 27 it was found that a system lubricated with Fomblin-Z octadecylamine had a lower friction coefficient than AM, DOL, and DIAC samples. It is, however, not feasible to compare our data directly to the results for these systems in ref 27, where the sliding occurred in contact with a large number of particles.…”

Section: Discussionmentioning

confidence: 99%

“…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%

“…[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][38][39][40] It has been found experimentally that the introduction of carboxyl, hydroxyl, or piperonyl end groups increases the ability of the Fomblin-Z polymer to protect the underlying substrate against wear. [19][20][21][22][23][24][25][26][27][28][29] It has been demonstrated that these polar end groups are preferentially located near the polar surface of the hydrogenated carbon overcoat that forms the top layer of the computer hard disk 22, [30][31][32]39,40 and also that they are located near other polar surfaces such as silica 21,23,33,34,41 and ZrO 2 . 42 Heating ("thermal bonding") introduces chemical bonds between functionalized chain ends and polar groups on the surface to further improve the stability of the lubricant film.…”

Section: Introductionmentioning

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%

“…42 Heating ("thermal bonding") introduces chemical bonds between functionalized chain ends and polar groups on the surface to further improve the stability of the lubricant film. 19,[21][22][23][24][25]28,29,39,40 For the low molecular weight polymers (2000-4000 g mol -1 ) currently utilized in magnetic storage devices, the polar end groups constitute a large fraction of the whole sample and affect strongly or even dominate the bulk properties of the sample, a phenomenon called the "copolymer effect". 43,44 In the study described below, we demonstrate that not only the affinity of the end groups for a polar surface but also the different structures that can be inferred for confined films containing different polar moieties in a nonpolar environment are critical for the performance of the film as a lubricant.…”

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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