Rayleigh scattering in a liquid far from thermal equilibrium

Abstract

We report the results of Rayleigh-scattering experiments in liquid toulene that is subjected to a stationary temperature gradient, but which otherwise is kept in a quiescent state. The measurements were made with temperature gradients up to 224 K/cm and scattering angles down to 0.45°. They probe fluctuations with wavelengths up to 40 μm and demonstrate the presence of long-range fluctuations in a nonequilibrium liquid. The strength of the observed nonequilibrium heat-mode and viscous-mode fluctuations varies with the square of the temperature gradient and with the fourth power of the wavelength of the fluctuations, in agreement with the behavior predicted by fluctuating hydrodynamics.