The relationship between domain structures and viscoelastic properties of a 1:1 blend of two immiscible polymers under steady shear flow and after step increase of shear rate were studied. The sample was a mixture of polydimethylsiloxane and polyisoprene which have almost the same viscosity. At steady states, domains were elipsoidal and their diameters were rather uniform and inversly proportional to shear rate. The shear stress and first normal stress difference were almost proportional to shear rate. After a step increase of shear rate, domains in the initial steady state were extremely elongated, which then ruptured to shorter ones and gradually changed to the final steady-state structure. An undershoot of shear stress and an overshoot of normal stress followed by a gradual change to steady-state values were observed during these processes. These results can be qualitatively explained by the change in the distribution of unit normal vectors of the interface.
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