General shear-thinning dynamics of confined fluids

Shinji Yamada

Research output: Contribution to journalArticle

52 Citations (Scopus)

Abstract

The shear properties for a number of thin fluid films under high pressure were investigated as a function of sliding velocity (shear rate) using the surface forces apparatus. It was found that the relationship between the effective viscosity ηeff and shear rate γ̇ in the shear-thinning regime could be expressed by a simple equation, log10 ηeff =C - nlog10γ̇, where C ≈ 4.7 ± 0.2 and n ≈ 0.9 ± 0.1. This equation can be applied to a variety of fluid systems from simple liquids to polymer melts, which transition to glasslike phases in confined geometries. Since the effect of confinement on the "slowing down" of molecular motions is equivalent to that of decreasing temperature, this universally can be explained using conventional glass-transition theories for bulk fluids. Assuming the confined fluid to be in a state where dynamics are dominated by excluded volume effects, its ηeff should correspond to that of the bulk at or near the glass-transition temperature. Thus, characteristic relaxation times in the system should correlate with the time scales of the primary relaxation processes associated with submolecular rearrangements, which are an essential feature of the glass transition and not very different for various fluid materials.

Original languageEnglish
Pages (from-to)167-171
Number of pages5
JournalTribology Letters
Volume13
Issue number3
DOIs
Publication statusPublished - 2002 Dec 1

Keywords

  • Confinement-induced glasslike transition
  • Shear thinning
  • Surface forces apparatus
  • Thin fluid films

ASJC Scopus subject areas

  • Mechanics of Materials
  • Mechanical Engineering
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films

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