Transition from metastability to instability in the dynamics of phase separation

We present results from a numerical study of the Cahn-Hilliard-Cook model in two dimensions. We study the transition from metastability to instability in this model by systematically changing the quench depth for an off-critical quench condition. We use different kinetic probes in the simulation to distinguish between two types of growth mechanisms: nucleation and spinodal decomposition. Although we can distinguish between nucleation and spinodal decomposition in some cases, the transition between these two growth processes is gradual. We do not see any evidence of a sharp transition from one to the other at the mean-field spinodal line. Actually, the center of the diffuse transition zone that we find in the simulation is located above the mean-field spinodal line. These features of the transition zone agree extremely well with analytical theories and with recent experiments.