Retraction of rod-like and spheroidal droplets and stress relaxation after step shear strain in polymer blends

Abstract

After application of a large step shear strain, a polymer droplet in an immiscible polymer matrix takes rod-like and spheroidal shapes before returning to the spherical shape. Change in semi axes of those droplets is calculated based on the Cohen-Carriere theory and the extension of the theory by Okamoto et al. From comparison with experimental data, it has been found that retraction of semi axes is well described by the theory using a hydrodynamic factor for the droplet associated with the viscous resistance of the matrix. The excess shear stress for rod-like and spheroidal droplets is predicted based on the Doi-Ohta theory by evaluating the interface tensor from the semi axes calculated. The predicted excess shear stress for the deformed droplet is close to experimental data of a polymer blend with narrow distribution of droplet size after normalization per one droplet with the volume-averaged radius. The effects of polydispersity and interaction with adjacent droplets in the blend are suggested for the remaining difference between the prediction and the data. © 2007 The Society of Rheology.