Phase separation kinetics during shear in compatibilized polymer blends

The effect of a diblock copolymer on the phase separation behavior of a polymer blend during shear was examined by light scattering. The phase: separation process in the mixtures was initiated by a slow cooling of the sample from the one-phase region into the two-phase region and various shear rates were applied to the samples simultaneously. These studies were designed to imitate behavior which may be encountered during injection molding or other manufacturing processes where mechanical deformation and phase separation may be superimposed on one another, thereby influencing the resultant blend morphology. Results were obtained for a model polystyrene and polybutadiene blend as a function of shear rate for two different final temperatures (shallow and deep quenches) in the two-phase region. Similar experiments were performed on a blend with a mass fraction of 2.5 percent of a symmetric diblock copolymer added. For the shallow quench, the pure blend exhibited an enhancement of the coarsening rate during shear over the quiescent coarsening rate while the modified blend showed ii suppressed coarsening rate during shear compared to the zero shear coarsening behavior. For the deeper quench, the pure blend exhibited a crossover in the coarsening from shear induced droplet breakup at low shear rates to shear enhanced coalescence at higher shear rates. The opposite behavior was observed for the modified blend, namely, shear enhanced coalescence at low shear rates, and shear induced droplet breakup (or suppressed coalescence) at higher shear rates.