Stress prediction for polymer blends with various shapes of droplet phase

The excess shear stress after application of large step strains in polymer blend is calculated from observed shapes of deformed droplets in immiscible matrix, based on the Doi-Ohta expression for the interface contribution to the stress. The calculation is made for droplet shapes of flat ellipsoid, rod with end caps, dumbbell and ellipsoid of revolution. The predicted excess relaxation modulus agrees very well with experimental data normalized per one droplet with the volume-averaged radius for a poly(isobutylene)/poly(dimethyl siloxane) blend with narrow distribution of droplet size. Especially, slow stress relaxation in the intermediate stage and faster relaxation thereafter predicted from the rod like and dumbbell shapes are consistent with the experimental data. For a blend of hydroxypropylcellulose solution/poly(dimethyl siloxane) with broad distribution of droplet size, the predicted excess relaxation modulus agrees reasonably well with experimental data by taking account of the size distribution.