Effect of shear history on the morphology of immiscible polymer blends

In this paper we study how the steady state morphology during shear of an incompatible blend can be affected by the initial conditions. By means of rheological experiments it is shown that below a critical shear rate multiple steady states can be obtained, the final morphology being then determined by the initial conditions of the blend. Above the critical shear rate the morphology is univocally determined by an equilibrium between break-up and coalescence. The critical shear rate is identified as the value at which the break-up limiting curve crosses the coalescence one. The applicability of different coalescence theories has been investigated by changing the viscosity ratio. The different coalescence theories can all describe the experimental results with a reasonable precision. The accuracy of the fully mobile interface theory seems to increase with decreasing viscosity ratio, whereas the opposite holds for the immobile interface theory. The partially mobile interface theory describes the various results equally well.