The Morphological Evolution Of Immiscible Polymer Blend Undercomplex Flow Field

It is an economical means to achieve desired product properties through blending immiscible polymers. In this process, the processing history strongly affects the morphology of the blends, accordingly exerts influence on the final properties of a blend. As a result, the relationship between flow and structure of immiscible blends is a topic of great meaning in guiding the actual processing.In this thesis, we analyzed the rheological and morphological evolution of polymer blend's under three kinds of complex flow fields. In addition, we discussed different microphases'contribution to the mechanical properties of polymer blend composed of viscoelastic components through separating their stress relaxation processes.Firstly, for parallel superposition flow in which a small amplitude oscillation is superimposed on a steady flow, we build a bridge between themorphological evolution and the moduli measured under this flow through developing an analytical model, in which the shape of the droplets is described with morphological tensor. Moreover, the calculated results based on this model agreed well with the results achieved in experiment on PIB/PDMS blend with the viscosity ratio 7.9.Secondly, the breakup and coalescence mechanics of dispersed droplets and its effect on the thixotropic behaviors are discussed. A new constitutive model (YZ model), in which breakup and coalescence of dispersed droplets are included, is applied in our discussion. A conclusion has been achieved that in experiment time too short for breakup to take place, the droplets size change highly depend on strain change. On the other side, in experiment time long enough for breakup and coalescence to take place during shearing, the droplets size change is closely related to the history of the flow field.Thirdly, a constitutive model by Yu and Bousmina has been applied in predict droplet shape evolution under large amplitude oscillation flow. Reasonably reproduction has been found in both the evolution of drop length and orientation angle. Detailed discussion has been given on nonlinearity.On the other side, exploration has been attempted on polymer blend composed of viscoelastic components. In start-up test followed by a relaxation process, viscous stress can be separated from elastic stress due to the difference in relaxing time of two processes. In addition, it has beenfound that the shear rate change in dispersed phase plays an important role in final mechanics of the polymer blends.