Morphology and Shear Viscosity for a Phase-separating Polymer Blend of Polybutadiene and Polyisoprene under Simple Shear Flow

The domain structure and shear viscosity of a phase-separated polymer blend of polybutadiene /polyisopreneare investigated with optical microscopy, light scattering, and rheometry. At the steady shear state, the shear-induced structures can be the nearly spherical droplets, the partially interconnected domains, the typical string-like domains, or the string-like domains with blurred interface, depending on the shear rate. The steady shear viscosity displays a rather non-Newtonian fluid behavior. In the transient flow experiments, the time dependence of viscosity and morphology after a stepwise increase of shear rate is studied and found to mainly depend on the final shear rate. In particular, as long as the final structures are the partially interconnected domains, the morphology evolution proceeds in the same way and the behaviors of the corresponding shear viscosity are similar.