Spinodal decomposition in a binary liquid mixture

Abstract

Light scattering was used to study phase separation near the critical temperature Tc in a critical mixture of 2,6-lutidine and water. This system has an inverted coexistence curve, so that a quench into the two-phase region is produced by an upward jump in temperature. The scattered intensity ℐ (q,t) was recorded at various angles and at a number of quench depths ΔTf =Tf−Tc in the range 0.5≲ΔTf≲2.5 mK. Here Tf denotes the final temperature. The initial temperature was also varied, and no initial-state effects were observed. One set of experiments employed a cell of very short optical path (0.1 mm) to minimize multiple scattering at the sacrifice of quenching speed. In another set, emphasis was placed on achieving a temperature jump in roughly 0.1 sec so that phase separation could be followed in its early stages. For ΔTf≲1 mK, the change in the measured ring diameter (qm−1) with time, is in fair agreement with the nonlinear theory of Langer, Bar-on, and Miller. However, the intensity of the ring, ℐ (qm,t), increases faster than this theory predicts. The measurements also reveal that the results depends significantly on the quench rate as well as quench depth.