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(a crylonitrile-co-styrene) was investigated by time-resolved light scatt ering during isothermal spinodal decomposition (SD) after a temperatur e 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 anot her 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 wa s apparent. Numerical calculation with a Cahn-Hilliard type nonlinear diffusion equation revealed that the apparent linear regime accidental ly appeared for a system with particular sets of kinetic parameters. T he late stage of demixing was well described by the recent scaling the ories; time evolution of the scaled wavenumbers of dominant Fourier co mponents in concentration fluctuations yielded a master curve, and a u niversal scaled structure function was seen.