Late-stage phase separation and hydrodynamic flow in a binary liquid mixture

Light-scattering measurements were made in a binary mixture in the late stage of spinodal decomposition, when gravity has become important. We observe macroscopic flow in the mixture, following which the scattering I(k,t) falls as k-4. This implies that the scattering is mainly from surfaces between growing domains. The measurements reveal an unexpectedly large rate of disappearance of the surface area per unit volume in the phase-separating system. The effect is probably related to a gravity-driven instability which gives rise to the flow and which was also investigated.