Rheology of polymer blends containing core-shell droplets

The core-shell composite droplets with well-designed functionality and morphology are widely used in polymer blends. Although great progress has been achieved in modeling the rheology of viscoelastic binary emulsions, no such model has been proposed to predict the rheology of ternary blends containing core-shell droplets. In this work, a ternary core-shell emulsion (CSE) model was developed to predict the linear viscoelasticity of ternary core-shell blends. The components’ contribution to the stress was evaluated from the velocity gradient in three domains. The evolutions of core-shell interface and shell-matrix interface were solved under small amplitude oscillatory shear, leading to the stress contribution from the two interfaces. Two impact polypropylene copolymers (IPCs), as a typical polymer containing core-shell droplets, were selected to validate the new model. Three components, including homopolypropylene matrix, ethylene–propylene block copolymer (core domain), and ethylene–propylene random copolymer (shell domain), were separated using a good solvent at different temperatures, and their rheology behavior was investigated. The new CSE model can accurately describe the components’ contribution to the linear rheology of IPCs, while the interfacial contribution of the CSE model is lower than the experimental data due to the agglomerated nature of core-shell droplets in IPCs. Because the components’ contribution dominates at high frequency, this work can be used to approximate the nonlinear steady-shear viscosity and first normal stress difference of core-shell ternary blends at high shear rates using the Cox–Merz rule and Laun's rule, respectively. Thus, the CSE model can guide the design of core-shell morphology with desired rheological properties.