Immiscible polymer blends: Processing and blend structure

Immiscible polymer blends are used increasingly as an alternative for synthesizing totally new polymers. Blend properties in general and their flow behaviour in particular remain largely unknown owing to their complex microstructure. Due to the presence of an interface, they display a flow behaviour that differs from that of pure polymers. The present study focuses on the steady state shear now of two-phase polymer blends. Mixtures of poly(isobutene) and poly(dimethylsiloxane), that are liquid at room temperature, have been used as model systems. The viscosity and especially the elasticity of blends show a significant increase as compared with a linear mixing rule for the contribution of the pure components. The effect of shear rate, concentration and viscosity ratio on the steady shear characteristics has been studied experimentally and the results have been compared with predictions of suspension and emulsion models. The results of the emulsion model of Choi and Schowalter have been found to be satisfactory for both viscosity and normal stress of various systems with up to 10% of disperse phase.