Binary miscible blends of poly(methyl methacrylate)/poly(α-methyl styrene-co-acrylonitrile):: II.: Rheological behavior during phase-separation

Rheological behavior of blends of poly(alpha-methylstyrene-co-acrylonitrile) (PalphaMSAN) and poly(methyl methacrylate) (PMMA) has been thoroughly investigated in the vicinity of the phase-separation temperatures. The characteristic rheological parameters of the blends, such as, dynamic shear moduli, G', G", and dynamic shear viscosity, eta* were found to be very sensitive to the phase change from one-phase to two-phase. A spinodal phase diagram was detected theologically using the theoretical approach of Ajji and Choplin. In addition, the correlation length, as a function of temperature, was also calculated for different blend compositions. The correlation length was found to increase drastically at the phase-separation temperature as a result of concentration fluctuations giving rise to an anomalous contribution to the viscoelastic properties. Furthermore, the time-resolved measurement of dynamic storage modulus (G') for the near-critical composition (PalphaMSAN/PMMA = 25/75) has been investigated as a function of temperature in the two-phase regime. The value of G' at constant temperature and shear rate (0.5 sec(-1)) was found to be unchanged in the one-phase regime. However, on the other hand, a decrease in the value of G' was observed with the beginning of spinodal decomposition. The magnitude of decrease in the value of G' was found to be temperature (quenching depth) dependent. The larger the value of the quenching depth, the larger the decrease in the magnitude of G' and the shorter the time required for the phase-separation process. Some of kinetic parameters of phase-separation, such as activation energy and rate constant, were calculated from the current method.