Morphology development of immiscible polymer blends in complex flow fields

To optimize the properties of immiscible blend products, the control of the blend microstructure is crucial. The goal of this thesis is to examine morphology development in realistic processing flows. Further, the degree in which the fundamental knowledge obtained in simple flow fields can be applied in complex environments is assessed. A slit-contraction flow cell generates the flow fields of interest. Small angle light scattering (SALS) characterizes the morphology in a model blend system of polyisobutene and polydimethylsiloxane. A SALS routine is developed to qualitatively describe the average deformation level in the blend in real time so that rapid structural transients can be tracked.; Under steady state operating conditions, droplet deformation is found to increase with decreasing droplet-to-matrix viscosity ratio (p) regardless of the flow geometry. As p increases, the elongational component of the mixed flow field becomes more important, The effects of transient flow are to overextend the droplet structure, increase the ability of shear to disperse high p blends, and cause a stronger shear thinning behavior in concentrated blend systems. Simple flow, steady state deformation models qualitatively describe the deformation process in complex flow situations and can predict the effects of parametric changes in the blend processing operation.; The transient structural evolution during coalescence is tracked. Both the rate and the overall change in magnitude of the droplet size increase with decreasing p. A new technique to characterize the degree of coalescence by inducing droplet break-up is developed. Coalescence is observed at extremely dilute droplet concentrations indicating an increased coalescence efficiency in complex flow fields. The kinetics of the process are described by a simple shear coalescence model when the average deformation rate in the mixed flow field is used. Coalescence in concentrated systems results in measurable stress transients during the droplet break-up process.; Extremely deformed structures are observed in a blend of polyisobutene and polybutadiene. SALS is used to characterize the break-up process of these extended threads. Droplet sizes are extracted from the scattering patterns, and break-up times in concentrated systems are found to be orders of magnitude longer than isolated thread break-up models. The SALS method is able to track a pressure-induced phase transition in the blend during the relaxation process.