Abstract
We investigate experimentally the effect of steady-state simple shear flow on the miscibility of a 60–40 poly(styrene-co-acrylonitrile) with poly(methyl-methacrylate) (PSAN/PMMA) blend. Thin disks, containing 60% w/w PSAN, are thermoformed from blend pellets made by mixing PSAN and PMMA granules in a co-rotating, fully-intermeshing twin-screw extruder. These disks are sheared at constant shear rate in a cone-and-plate mechanical spectrometer at fixed temperatures within the quiescent two-phase region. At the end of each shearing experiment the sample is quenched and its morphology investigated first visually for optical transparency (cloudiness being an indicator of a phase-separated blend) and then using transmission electron microscopy (TEM). Results indicate that upon imposition of a shear rate as low as 0.1s−1 the 60–40 blend remains miscible even at temperatures up to 7K within the (quiescent) two-phase region. These observations are in agreement with theoretical predictions of the phase diagram under shear, based on the concept of a modified Gibbs free energy of mixing. The TEM results concerning the morphology of the phase-separated blends are also discussed.
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