Shear influences on the phase separation of blends made of homopolymer A and random copolymer A-B

Shear induced changes in the demixing conditions are discussed for the copolymer blends of the present type in terms of a distortion of quasichemical equilibria established in the stagnant systems between the two different kinds of polymer segments. Calculations were performed in an attempt to rationalize experimental results obtained with blends exhibiting upper critical solution temperatures. The proposed model accounts for the experience that the first observable effect of shear consists of an enlargement of the two-phase regime (a behavior which differs fundamentally from that of homopolymer blends or homopolymer solutions) and yields the correct order of magnitude for the effects. The influences of copolymer composition, number of segments of the components, and temperature dependence of the Flory-Huggins interaction parameter are discussed in detail. Furthermore, it is demonstrated how the present considerations relate to an earlier approach based on the energy a system can store while it flows. (C) 1999 American Institute of Physics. [S0021-9606(99)50115-3].