Light scattering was used to study phase separation near the critical temperatureTcin a critical mixture of 2,6hyphen;lutidine and water. This system has an inverted coexistence curve, so that a quench into the twohyphen;phase region is produced by an upward jump in temperature. The scattered intensityI(q,t) was recorded at various angles and at a number of quench depths Dgr;Tf=Tfminus;Tcin the range 0.5lsim;Dgr;Tflsim;2.5 mK. HereTfdenotes the final temperature. The initial temperature was also varied, and no initialhyphen;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 Dgr;Tflsim;1 mK, the change in the measured ring diameter (qmminus;1) with time, is in fair agreement with the nonlinear theory of Langer, Barhyphen;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.
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