DEMIXING KINETICS IN A BINARY POLYMER MIXTURE OF POLY(METHYL METHACRYLATE) AND POLY(ACRYLONITRILE-CO-STYRENE)

Demixing kinetics in a mixture of poly(methyl methacrylate) and poly(acrylonitrile-co-styrene) was investigated by time-resolved light scattering during isothermal spinodal decomposition (SD) after a temperature jump from the single-phase region to the two-phase region above the lower critical solution temperature. Two linear regimes were found; i.e., scattered intensity increased exponentially at first and then another exponential increase was observed. When the kinetics were analyzed in more detail on the basis of the linearized theory of SD, the first regime was assigned to the early stage of SD, while the second one was apparent. Numerical calculation with a Cahn-Hilliard type nonlinear diffusion equation revealed that the apparent linear regime accidentally appeared for a system with particular sets of kinetic parameters. The late stage of demixing was well described by the recent scaling theories; time evolution of the scaled wavenumbers of dominant Fourier components in concentration fluctuations yielded a master curve, and a universal scaled structure function was seen.