Shear thinning near the critical point of xenon

Robert F. Berg, Michael R. Moldover, Minwu Yao, and Gregory A. Zimmerli
Phys. Rev. E 77, 041116 – Published 17 April 2008; Erratum Phys. Rev. E 79, 039901 (2009)

Abstract

We measured shear thinning, a viscosity decrease ordinarily associated with complex liquids, near the critical point of xenon. The data span a wide range of reduced shear rate: 103<γ̇τ<700, where γ̇τ is the shear rate scaled by the relaxation time τ of critical fluctuations. The measurements had a temperature resolution of 0.01 mK and were conducted in microgravity aboard the Space Shuttle Columbia to avoid the density stratification caused by Earth’s gravity. The viscometer measured the drag on a delicate nickel screen as it oscillated in the xenon at amplitudes 3μm<x0<430μm and frequencies 1Hz<ω/2π<5Hz. To separate shear thinning from other nonlinearities, we computed the ratio of the viscous force on the screen at γ̇τ to the force at γ̇τ0: CγF(x0,ωτ,γ̇τ)/F(x0,ωτ,0). At low frequencies, (ωτ)2<γ̇τ, Cγ depends only on γ̇τ, as predicted by dynamic critical scaling. At high frequencies, (ωτ)2>γ̇τ, Cγ depends also on both x0 and ω. The data were compared with numerical calculations based on the Carreau-Yasuda relation for complex fluids: η(γ̇)/η(0)=[1+Aγ|γ̇τ|]xη/(3+xη), where xη=0.069 is the critical exponent for viscosity and mode-coupling theory predicts Aγ=0.121. For xenon we find Aγ=0.137±0.029, in agreement with the mode coupling value. Remarkably, the xenon data close to the critical temperature Tc were independent of the cooling rate (both above and below Tc) and these data were symmetric about Tc to within a temperature scale factor. The scale factors for the magnitude of the oscillator’s response differed from those for the oscillator’s phase; this suggests that the surface tension of the two-phase domains affected the drag on the screen below Tc.

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  • Received 27 September 2007

DOI:https://doi.org/10.1103/PhysRevE.77.041116

Erratum

Erratum: Shear thinning near the critical point of xenon [Phys. Rev. E 77, 041116 (2008)]

Robert F. Berg, Michael R. Moldover, Minwu Yao, and Gregory A. Zimmerli
Phys. Rev. E 79, 039901 (2009)

Authors & Affiliations

Robert F. Berg and Michael R. Moldover

  • National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA

Minwu Yao

  • Ohio Aerospace Institute, Cleveland, Ohio 44142, USA

Gregory A. Zimmerli

  • NASA Glenn Research Center, Cleveland, Ohio 44135, USA

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Issue

Vol. 77, Iss. 4 — April 2008

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