Viscous behavior and mixing rules for an immiscible model polymer blend

In this work the viscosity of a model blend, composed of poly-isobutene and polydimethyilsiloxane, has been measured at two different temperatures and for a wide range of blend compositions and shear rates. Cone and plate and capillary measurements showed a good overlap in the shear rate window acce ssible to both instruments. The experimental results have been compared to the predictions of two emulsion models [Frankel and Acrivos (1970), Choi an d Schowalter (1975)], and of some simple, empirical mixing rules. Good quan titative agreement was found between the data and the Frankel-Acrivos model , once the correct dependency of the droplet radius upon shear rate is acco unted for. To this end, droplet radii were independently determined by visc oelastic measurements upon cessation of steady shear flow. The Frankel-Acri vos 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. (C) 2000 The Society of Rheology. [S014 8-6055(00)00901-9].