Shear viscosity of phase-separating polymer blends with viscous asymmetry - art. no. 061403

Rheo-optical measurements of phase separating polymer mixtures under simple shear flow have been used to investigate the influence of domain morpholog y on the viscosity of emulsionlike polymer blends, in which the morphology under weak shear is droplets of one coexisting phase dispersed in a matrix of the second. The structure and viscosity of low-molecular-weight polybuta diene and polyisoprene mixtures, phase separated by quenching to a temperat ure inside the coexistence region of the phase diagram, were measured as a function of shear rate and composition. In the weak shear regime, the data are in qualitative agreement with an effective medium model for non-dilute suspensions of slightly deformed interacting droplets. In the strong shear regime, where a stringlike pattern appears en route to a shear-homogenized state, the data are in qualitative agreement with a simple model that accou nts for viscous asymmetry in the components.