Shear effect on the phase behaviour and morphology in oligomer blend of polystyrene/poly(methyl methacrylate)

The phase behaviour of an oligomer mixture of polystyrene/poly(methyl metha crylate) (PS/PMMA), which shows an upper critical solution temperature (UCS T) type phase diagram, has been investigated under simple shear flow. The c loud points were strongly affected by the values of the applied shear rate. The phase diagrams under different values of shear rate, indicated shear-i nduced mixing for all measured compositions, and the magnitudes of the depr ession of the cloud points under the effect of shear rate were found to be composition dependent. The dramatic decrease of the homogenization temperat ure was investigated as a function of shear rate ((gamma) over dot), and th e normalised shift in the cloud point \DeltaT((gamma) over dot)/T(0)\ versu s (gamma) over dot was also studied and compared with that of simple liquid mixtures and polymer solutions, as well as high molecular weight polymer b lends. The cloud points of this oligomer mixture showed high sensitivity to change under the effect of shear rate; a much higher sensitivity than both simple liquid mixtures and polymer solutions, on the other hand, slightly less sensitivity than the high molecular weight polymer blend (PMMA/poly(st yrene-co-acrylonitrile)). The morphology of PS/PMMA = 30/70 blend was also studied under different values of shear rate at 35 degreesC below its quies cent cloud point, using the transmission electron microscopy (TEM). The res ults showed that the shear-induced mixing occurred at a high critical shear rate value (34 s(-1)), below which the dispersed PS-rich domains were slig htly elongated and broken-up into very small domain sizes with very good pa rticle distribution. (C) 2000 Published by Elsevier Science Ltd.