Time-resolved light scattering studies on kinetics of phase separation and phase dissolution of polymer blends. 1. Kinetics of phase separation of a binary mixture of polystyrene and poly(vinyl methyl ether

ABSTRACT The dynamics of liquid-liquid phase separation of a polymer blend of polystyrene and poly(viny1 methyl ether) was studied by time-resolved elastic light scattering techniques in both the nucleation-growth (NG) and spinodal-decomposition (SD) regimes. It was found that in the early stage of SD the scattered intensity a t a given momentum transfer q = (4r/X) sin (8/2) increases exponentially with time after the initiation of the isothermal phase separation involved by a temperature jump from the temperature well below the binodal point. The relaxation rate 2R(q) of the intensity increase is a function of q such that R(q)/q2 linearly decreases with q2, in accord with the linear theories of SD originally proposed by Cahn for small molecules and extended by de Gennes for polymers. The spinodal temperature was obtained from the dynamics measured as a function of temperature in the linear SD regime. In the later stage of SD, the intensity increase with time starts to deviate from exponential behavior and the scattering maximum shifts to smaller q, corresponding to the onset of the coarsening process. The higher the superheating, the earlier the stage where the coarsening starts. In the NG regime the intensity increases nonexponentially with time