Frequency-Dependent Viscosity of Xenon Near the Critical Point

Published

October 1, 1999

Author(s)

Robert F. Berg, Michael R. Moldover, G A. Zimmerli

Abstract

We used a novel, overdamped oscillator aboard the Space Shuttle to measure the viscosity Η of xenon near its critical density ρ_c and temperature T_c. In microgravity, useful data were obtained within 0.1 mK of T_c, corresponding to a reduced temperature t = (T - T_c ) / T_c = 3x10^-7. Because they avoid the detrimental effects of gravity at temperatures two decades closer to T_c than the best ground measurements, the data directly reveal the expected power-law behavior (Η{variation}t-υζΗ^). Here υ is the correlation length exponent, and our result for the small viscosity exponent is ζ_Η = 0.0690 ± 0.0006. (All uncertainties are one standard uncertainty.) Our value for ζ_{Η depends only weakly on the form of the viscosity crossover function, and it agrees with the value 0.067 ± 0.002 obtained from a recent two-loop perturbation expansion [H. Hao, R.A. Ferrell, and J.K. Bhattacharjee, (unpublished)]. The measurements spanned the frequency range 2 Hz {u-5^, further from Tc than predicted. The viscoelasticity's frequency dependence scales as Afτ, where τ is the fluctuation-decay time. The fitted value of the viscoelastic time-scale parameter A is 2.0 {+or -} 0.3 times the result of a one-loop perturbation calculation. Near Tc , the xenon's calculated time constant for thermal diffusion exceeded days. Nevertheless, the viscosity results were independent of the xenon's temperature history, indicating that the density was kept near ρc by judicious choices of the temperature vs. time program. Deliberately bad choices led to large density inhomogeneities. At t >10^-5, the xenon approached equilibrium much faster than expected, suggesting that convection driven by microgravity and by electric fields slowly stirred the sample.}

Citation

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics)

Volume

60

Pub Type

Journals

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Keywords

critical point, microgravity, viscoelasticity, viscoelasticity, viscosity exponent, xenon

Citation

Berg, R. , Moldover, M. and Zimmerli, G. (1999), Frequency-Dependent Viscosity of Xenon Near the Critical Point, Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=832041 (Accessed April 25, 2024)