THE DYNAMICS OF PHASE-SEPARATION IN A POLYMER MIXTURE OF CRITICAL COMPOSITION - THE EFFECT OF TEMPERATURE

The dynamics of phase separation of a polymer mixture of critical composition was simulated on a simple square lattice using nonlinear Cahn-Hillard equation assuming that the mobility of the components is controlled by their concentrations. The data on variation of the mean dimensions of the elements of phase structure, interfacial area, thickness of interfacial layer, and structural factor during spinodal decomposition were obtained for different values of the Flory-Huggins parameter chi. Four stages of the process may be distinguished: the early, intermediate, transient, and final stages, each showing inherent kinetic features. For the time span corresponding to the intermediate stage (and the examined interval of chi values), the increase in the mean dimensions of the elements of the phase structure cannot be represented with a universal plot. Beginning from the transient stage of the process, time variations of the mean dimensions of phase particles and of the interfacial area are described by the same exponential law. The thickness of interfacial layer reaches an equilibrium value during the transient stage of the process. In spite of the fact that attainment of equilibrium concentrations (determined by the Flory-Huggins equation) by each of the forming phases is significantly slowed down, because the mobility in the Cahn-Hillard equation is concentration-dependent, the scaling function becomes universal (ensuring the validity of the dynamic scaling law) at the final stage of the process, when the mean dimensions of phase particles are much greater than the thickness of interfacial layer.