Viscous Behaviour and Mixing Rules for an Immiscible Model Polymer Blend

In this work the viscosity of a model blend, composed of Poly-isobutene (PIB) and Poly-dimethyilsiloxane (PDMS), has been measured at two different temperatures and for a wide range of blend compositions and shear rates. Cone and plate and capillary measurements have been performed, showing a good overlap in the shear rate window accessible to both instruments. The experimental results have been compared to the predictions of two emulsion models (Frankel and Acrivos, 1970, Choi and Schowalter, 1975), and of some simple, empirical mixing rules. Good quantitative agreement was found between the data and the Frankel-Acrivos model, once the correct dependency of the droplet radius upon shear rate is accounted for. To this end, droplet radii were independently determined by viscoelastic measurements upon cessation of steady shear flow. Unlike the empirical mixing rules, the Frankel-Acrivos model is also able to predict the change from a positive to a negative deviation from the ideal mixing rule for increasing shear rates, which is a typical feature of polymer blends