Viscoelasticity of Xenon near the Critical Point

Using a novel, overdamped, oscillator flown aboard the space shuttle, we measured the viscosity of xenon near the liquid-vapor critical point in the frequency range $2\mathrm{Hz}\ensuremath{\le}f\ensuremath{\le}12\mathrm{Hz}$. The measured viscosity divergence is characterized by the exponent ${z}_{\ensuremath{\eta}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.0690\ifmmode\pm\else\textpm\fi{}0.0006$, in agreement with the value ${z}_{\ensuremath{\eta}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.067\ifmmode\pm\else\textpm\fi{}0.002$ calculated from a two-loop perturbation expansion. Viscoelastic behavior was evident when $t\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}({T\ensuremath{-}T}_{c}){/T}_{c}<{10}^{\ensuremath{-}5}$ and dominant when $t<{10}^{\ensuremath{-}6}$, further from ${T}_{c}$ than predicted. Viscoelastic behavior scales as $\mathrm{Af}\ensuremath{\tau}$ where $\ensuremath{\tau}$ is the fluctuation decay time. The measured value of $A$ is $2.0\ifmmode\pm\else\textpm\fi{}0.3$ times the result of a one-loop calculation. (Uncertainties stated are one standard uncertainty.)

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