Properties of Perfluoropolyethers for Space Applications

Jones, William

doi:10.1080/10402009508983442

Cited by 59 publications

(34 citation statements)

References 31 publications

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“…13,14 These fluids possess excellent thermal and chemical stability, low vapor pressure, and favorable lubricating properties. They are currently used as lubricants in aerospace [15][16][17] and laboratory ultrahigh vacuum equipment 18 and in magnetic storage devices (computer disk drives). There is considerable interest in further improvement of the lubricating properties of Fomblin-Z polymers and of their ability to protect sliding surfaces against wear.…”

Section: Introductionmentioning

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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Section: Introductionmentioning

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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“…In case of used fluid with molecular weight 5900, temporary viscosity loss did not occur at EHL inlet zone. Bair et al 16) and Jones 2) previously pointed out the shear thinning behavior in the EHL inlet zone of a linear PFPE Z25. Our experimental result is supported by their results.…”

Section: Discussionmentioning

confidence: 99%

“…Perfluoropolyether (PFPE) fluids are used on magnetic recording media 1) , aerospace industry and satellite instruments satisfactorily 2) . These fluids are also used as hydraulic fluids, high temperature liquid lubricants in turbine engines 3) , and base oils of high-temperature greases.…”

Section: Introductionmentioning

confidence: 99%

Viscosity Loss in PFPE Lubricant for Space Applications under EHL Conditions

et al. 2007

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An unbranched perfluoropolyether (PFPE) 815Z is the current ball bearing lubricant for space applications. Measurements of elastohydrodynamic lubrication (EHL) oil film thickness have been carried out to assess the lubricating performance of PFPE with average molecular weight of 9200 using an optical interferometric technique under mean Hertzian pressure 0.45 GPa. The film thickness of 815Z became less than predicted film thickness from Hamrock and Dowson formula for EHL central film thickness. There are two main explanations why PFPE is inferior to mineral oil in their ability to form EHL films, temporary viscosity loss and permanent viscosity loss. In order to elucidate the results, measurements of permanent viscosity loss under mean Hertzian pressure from 0.41 GPa to 2.67 GPa have been carried out using the thrust ball bearing. There results show that the degree of the permanent viscosity loss depends on Hertzian pressure, occurrence of permanent viscosity loss of 36 % with 2.67 GPa and 2 % with 0.41 GPa.

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“…Therefore, only a few kinds of lubricants can be put to practical use in space mechanisms. Perfluoropolyether (PFPE) is one such lubricant, and many studies have already reported on its lubrication performance in space [1][2][3][4][5]. Multiplyalkylatedcyclopentane (MAC) is also a liquid lubricant used in space mechanisms, and its lubrication performance has also been studied thoroughly [6][7][8].…”

Section: Introductionmentioning

confidence: 99%

Lubrication Performance of Ionic Liquids as Lubricants for Space Mechanisms under High Vacuum and Low Temperature

et al. 2015

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The objective of this study is to evaluate the boundary lubrication performance of ionic liquids under high vacuum and low temperature by taking the cosmic space environment into consideration, as a screening stage prior to evaluating lubrication performance in actual space mechanisms. The boundary lubrication performance of ionic liquids was evaluated at room temperature with a reciprocating linear motion tribometer, and at low temperature (from −80°C to room temperature) with a unidirectional rotation tribometer. Low-temperature rheometry was also carried out. Ionic liquids showed a supercooling state and crystallization. This crystallization was prevented by mixing different ionic liquids together. The equimolar mixture of 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl) amide (EMI-TFSA), 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl) amide (BMI-TFSA), and 1-hexyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl) amide (HMI-TFSA) showed no crystallization in our experiment. The antiwear performance of this sample oil mixture was similar to that of MAC and much better than that of PFPE at low temperatures. This mixture prevented metal contact at −80°C, most likely due to its high viscosity and high adsorption of molecules.

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Properties of Perfluoropolyethers for Space Applications

Cited by 59 publications

References 31 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

Viscosity Loss in PFPE Lubricant for Space Applications under EHL Conditions

Lubrication Performance of Ionic Liquids as Lubricants for Space Mechanisms under High Vacuum and Low Temperature

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