PHASE-SEPARATION DYNAMICS IN A CONCENTRATION GRADIENT

Phase separation dynamics with an initially nonunifom concentration ar e studied. critical and off-critical behavior is observed simultaneous ly. A mechanism for an expanding phase-separated region is demonstrate d and the time dependence of the concentration is determined. The fina l equilibrium state consists of a planar interface separating one phas e from the other. The evolution to this state is characterized by an e xperimentally observable flux, j, crossing this interface. We find tha t j approximately t-2/3 if patterns are formed in the bulk and j appro ximately t-1/2 if the bulk remains homogeneous. The results are explai ned in terms of scaling arguments which are confirmed numerically.