Study of non-Newtonian polymer blends using large amplitude oscillatory shearing flow

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.

Computational Predictions for Boger Fluids and Circular Contraction Flow under Various Aspect Ratios

This work puts forward a modeling study contrasted against experimental, with focus on abrupt circular contraction flow of two highly-elastic constant shear-viscosity Boger fluids, i.e., a polyacrylamide dissolved in corn-syrup PAA/CS (Fluid-1) and a polyisobutylene dissolved in polybutene PIB/PB (Fluid-2), in various contraction-ratio geometries. Moreover, this work goes hand-in-hand with the counterpart matching of experimental pressure-drops observed in such 4:1 and 8:1 aspect-ratio contraction flows, as described experimentally in the literature. In this study, the experimental findings, for Boger fluids with severe strain-hardening features, reveal significant vortex-evolution characteristics, correlated with enhanced pressure-drop phasing and normal-stress response in the corner region. It is shown how such behavior may be replicated through simulation and the rheological dependencies that are necessary to bring this about. Predictive solutions with an advanced hybrid finite-element/volume (fe/fv) algorithm are able to elucidate the rheological properties (extensional viscosity and normal-stress response) that rule such vortex-enhancement evolution. This is accomplished by employing the novel swanINNFM(q) family of fluids, through the swIM model-variant, with its strong and efficient control on elongational properties.