Viscous Damping of Thermal Excitations on the Interface of Critical Fluid Mixtures

Measurements of the time-dependent correlation function for small-angle scattering of visible light by the interface in a fluid mixture to within 3×{}10^-3^∘{}K of its critical temperature Tc have revealed thermal excitations with exponential relaxation times τ up to about 20 sec. Analysis has shown that τ varies inversely as the wave number Q and diverges on approaching the critical temperature as (1-TTc)^-1.27. Identification of τ with viscous damping of hydrodynamic waves on the interface permits determination of the critical behavior of the shear viscosity which is found to be at most only weakly divergent.