PHASE-SEPARATION DYNAMICS IN A CONCENTRATION GRADIENT

Phase separation dynamics with an initially nonunifom concentration are studied. critical and off-critical behavior is observed simultaneously. A mechanism for an expanding phase-separated region is demonstrated and the time dependence of the concentration is determined. The final equilibrium state consists of a planar interface separating one phase from the other. The evolution to this state is characterized by an experimentally observable flux, j, crossing this interface. We find that j approximately t-2/3 if patterns are formed in the bulk and j approximately t-1/2 if the bulk remains homogeneous. The results are explained in terms of scaling arguments which are confirmed numerically.