No abstract

Large amplitude oscillatory shear (LAOS) was performed on non-Newtonian minor phase in Newtonian matrix phase polymer blends as a first step toward understating more complex immiscible polymer blends under high deformation condition. The blend consists polybutadiene (PBD) as the droplet phase and polydimethylsiloxane (PDMS) as the matrix phase. The PBD droplet phase was an elastic “Boger” fluid prepared by dissolving a high-molecular-weight PBD into a low-molecular-weight Newtonian PBD. Different percentages of the high-molecular-weight PBD were used to prepare different types of Boger fluids that resulted in blends with different viscosity ratios from lower than unity, to unity and higher than unity. Furthermore, the LAOS results of the blends were analyzed by using the Fourier Transform (FT) technique. From a theoretical point of view, the constrained volume model (CV-model) for Newtonian components is adapted to the case of a Newtonian matrix phase and non-Newtonian Boger fluid droplet phase by taking into account stresses that arise in the Boger fluids. The adapted model and the Newtonian CV-model were compared to the experimental results of FT-LAOS for checking the predictability of the model against the rheological properties. The adapted model shows some reasonable qualitative and quantitative agreements at high strain amplitude values.

In this work, we carried out numerical modeling of the large deformation of a shear thinning droplet suspended in a Newtonian matrix using the constrained volume model. The adopted approach was to consider making incremental corrections to the evolution of the droplet anisotropy equation in order to capture the experimental behavior of a shear thinning droplet when subjected to deformation due to imposed flow. The constrained volume model was modified by using different models to describe the viscosity of droplet phase: the Bautista et al. model, the Carreau-Yasuda model and the Power-law model. We found that by combining the constrained volume model with a simple shear thinning viscosity model we were able to describe the available experimental data for large deformation of a shear thinning droplet suspended in a Newtonian matrix. Moreover, we developed an equation approximating flow strength during droplet retraction, and we found that the model can accurately describe the experimental data of the retraction of a shear thinning droplet.