The effect of shear flow on the phase behavior of polybutadiene/polyisoprene blends

The parameters which control the miscibility of blends of amorphous polybutadiene and polyisoprene were investigated under equilibrium and flow conditions, using a combined rheometer and light scattering techniques. Quiescent light scattering cloud point measurements show that the blends are miscible at room temperature with the miscibility increasing with the vinyl content of polybutadiene. Temperature jump experiments were performed by heating the blend from a one-phase to two-phase region, followed by shearing while simultaneously monitoring the development of the scattering patterns and intensities. The results show dramatic differences in shear rate and shear strain dependent scattered intensities in two mutually orthogonal directions, parallel to and perpendicular to flow directions. These results are interpreted in the light of existing models for flow-induced phase behavior in polymer blends, including flow-induced miscibility and suppression of fluctuations by flow.