Tribology of confined Fomblin-Z perfluoropolyalkylethers: Molecular weight dependence and comparison between unfunctionalized and telechelic chains

Marina Ruths, Steve Granick

Research output: Contribution to journalReview articlepeer-review

Abstract

The dynamic shear properties of molecularly-thin films of unfunctionalized and end-functionalized (telechelic) Fomblin-Z perfluoropolyalkylether (PFPAE) melts with number-average molecular weight Mn ≈ 3000-4000 g mol-1 have been studied at shear rates of 10-2-105 s-1 at normal pressures of 1 and 3 MPa. The shear responses are compared to measurements on end-functionalized polymers of the same chemical composition but lower molecular weight, Mn ≈ 2000 g mol-1. The predominantly elastic response and high shear moduli of the confined film of unfunctionalized polymer, Fomblin Z03, suggest that it forms a structure likely to solidify already at low pressure. Its lubricating properties are less favorable than the ones found for hydroxyl- (DOL) and piperonyl-terminated Fomblin-Z (AM2001, AM3001), where associated molecules form a structure less prone to solidification under confinement. The thickness of the compressed films of the end-functionalized polymers increased more strongly with molecular weight than as Mn0.5. The shear moduli were found to be larger, the higher the molecular weight, indicating slower relaxations. At a normal pressure of 3 MPa, these films solidified and displayed stick-slip as seen already at 1 MPa in the Z03 film. The limiting shear stress of the unfunctionalized Z03, σ > 3 MPa, exceeded by an order of magnitude the limiting shear stress of all of the end-functionalized polymers. The limiting shear stress of the hydroxyl-terminated polymer was larger than that of the piperonyl-terminated polymer.

Original languageEnglish (US)
Pages (from-to)161-172
Number of pages12
JournalTribology Letters
Volume7
Issue number4
DOIs
StatePublished - 1999
Externally publishedYes

Keywords

  • End-functionalized Fomblin-Z
  • Molecular weight dependence
  • Rheological properties
  • Unfunctionalized Fomblin-Z

ASJC Scopus subject areas

  • General Chemical Engineering
  • Mechanical Engineering

Fingerprint

Dive into the research topics of 'Tribology of confined Fomblin-Z perfluoropolyalkylethers: Molecular weight dependence and comparison between unfunctionalized and telechelic chains'. Together they form a unique fingerprint.

Cite this