Very low-angle static light scattering from steady-state and time-dependent nonequilibrium fluctuations

Abstract

We investigate both steady-state and time-dependent nonequilibrium fluctuations by means of very low-angle static light scattering. The system is a thin layer of a binary liquid mixture close to a critical consolution point and placed in a temperature gradient. Due to this choice, the Soret driven nonequilibrium fluctuations are large and their time evolution is slow enough to be followed at ease. We discuss the fast q divergence at steady state and its low q frustration induced by the presence of gravity. We also report measurements taken during the build-up of the concentration gradient. The data indicate that no additional contributions are present during the time-dependent part of the process beyond those calculated in the quasi-steady-state approximation.