Rayleigh scattering from liquids, liquid mixtures, and polymer solutions in nonequilibrium steady states

This dissertation is concerned with nonequilibrium fluctuations as measured by small-angle dynamic light scattering in various liquid systems. Both mode-coupling theory and nonequilibrium fluctuating hydrodynamics predict that long-range molecular correlations are present in a liquid subjected to a stationary temperature gradient {dollar}nabla T{dollar}, even when the system is far from a critical point or from a hydrodynamic instability. These long-range correlations enhance and modify the spectrum of the scattered Rayleigh light because of mode-coupling effects. More specifically, the amplitudes of thermal-mode, viscous-mode, and concentration-mode nonequilibrium fluctuations are predicted to be proportional to ({dollar}nabla T)sp2/ksp4{dollar} where k is the scattering wave number.; In this dissertation, we review the theory of nonequilibrium fluctuating hydrodynamics in deriving the heterodyne correlation functions of the scattered-light intensity in a one-component and a two-component liquid systems. We also demonstrate how long-range nonequilibrium hydrodynamic fluctuations can be measured with small-angle Rayleigh light scattering. In particular, we present experimental results of light scattered from liquid n-hexane, mixtures of toluene + n-hexane, and dilute polymer solutions of polystyrene + toluene in equilibrium and nonequilibrium stationary states. Our experiments confirm that the enhancement of the light-scattering intensity for all diffusive modes in a liquid increases with ({dollar}nabla T)sp2/ksp4{dollar}. Attention is called to the effect of the spread of scattering angle due to finite size of the collection angle. The effect of spatial variations of the thermophysical properties on the Rayleigh spectrum is also discussed. A major achievement of this work is that we have measured for the first time nonequilibrium fluctuations in a polymer solution and have found that the measured fluctuations are in agreement with a theory recently presented by Schmitz for colloidal suspensions.