Viscoelasticity of xenon near the critical point

Using a novel, overdamped, oscillator flown aboard the space shuttle, we me asured the viscosity of xenon near the liquid-vapor critical point in the f requency range 2 Hz less than or equal to f less than or equal to 12 Hz. Th e measured viscosity divergence is characterized by the exponent z(eta) = 0 .0690 +/- 0.0006, in agreement with the value z(eta) = 0.067 +/- 0.002 calc ulated from a two-loop perturbation expansion. Viscoelastic behavior was ev ident when t = (T - T-c)/T-c < 10(-5) and dominant when t < 10(-6), further from T-c than predicted. Viscoelastic behavior scales as Af tau where tau is the fluctuation decay time. The measured value of A is 2.0 +/- 0.3 times the result of a one-loop calculation. (Uncertainties stated are one standa rd uncertainty.).