Light-scattering measurements of nonequilibrium fluctuations in a liquid mixture

Abstract

We report results of small-angle Rayleigh-scattering experiments performed in an equimolar liquid mixture of toluene and n-hexane that is brought out of thermal equilibrium by the imposition of a stationary temperature gradient ∇T perpendicular to the scattering wave vector. The experiments demonstrate the presence of long-range nonequilibrium fluctuations in temperature, concentration, and momentum and confirm that the strength of these nonequilibrium fluctuations varies with (∇T${)}^2$/${\mathit{k}}^4$, where k is the wave number of the fluctuations. It is suggested that nonequilibrium Rayleigh scattering may provide an alternative technique for measuring Soret coefficients of liquid mixtures.