RHEOLOGY OF POLYSTYRENE POLY(VINYL METHYL-ETHER) BLENDS NEAR THE PHASE-TRANSITION

Mixtures are expected to show anomalous behavior in their viscoelastic properties close to a critical point. In this study, the rheological behavior of blends of polystyrene and poly (vinyl methyl ether) below, close to, and above the phase separation temperature T(s) was investigated. Rheological measurements were carried out at three different compositions in the melt. Below and far from T(s), a satisfactory superposition of the storage and loss moduli G' and G" was observed at all temperatures and frequencies. Close to T(s), deviations were observed for G' at low frequencies (the so-called terminal zone). Above T(s), G' exhibited a plateau in the terminal region, whereas a satisfactory superposition of G" values was still observed over the whole range of frequencies and temperatures. The deviations observed for G' near T(s) can be interpreted as due to the presence of significant concentration fluctuations. Plots of log (G'/G"2) as a function of temperature were shown to be sensitive to this anomalous behavior.