Light-scattering measurements of entropy and viscous fluctuations in a liquid far from thermal equilibrium

We have performed small-angle Rayleigh-scattering measurements in toluene subject to a large stationary temperature gradient {∇}T. The experiments demonstrate the presence of long-range entropy and viscous fluctuations enhancing and modifying the Rayleigh spectrum. The experiments confirm that the viscous-heat-mode contributions vary with ({∇}T)²/q⁴, where q is the wave number of the fluctuations. The observed amplitudes of both the entropy and viscous fluctuations are in excellent agreement with the theoretical predictions for the fluctuations in nonequilibrium fluids.