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 $2\mathrm{Hz}\le f\le 12\mathrm{Hz}$. The measured viscosity divergence is characterized by the exponent $z_{\eta }=0.0690\mathrm{}\pm 0.0006$, in agreement with the value $z_{\eta }=0.067\mathrm{}\pm 0.002$ calculated from a two-loop perturbation expansion. Viscoelastic behavior was evident when $t=\left({T-T}_c\right){/T}_c<{10}^{-5\mathrm{}}$ and dominant when $t<\mathrm{}{10}^{-6\mathrm{}}$, further from $T_c$ than predicted. Viscoelastic behavior scales as $\mathrm{Af}\tau$ where $\tau$ is the fluctuation decay time. The measured value of $A$ is $2.0\pm 0.3$ times the result of a one-loop calculation. (Uncertainties stated are one standard uncertainty.)

• Received 2 November 1998

DOI:https://doi.org/10.1103/PhysRevLett.82.920