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 copo lymer blends of the present type in terms of a distortion of quasichemical equilibria established in the stagnant systems between the two different ki nds of polymer segments. Calculations were performed in an attempt to ratio nalize 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 homopolym er blends or homopolymer solutions) and yields the correct order of magnitu de for the effects. The influences of copolymer composition, number of segm ents of the components, and temperature dependence of the Flory-Huggins int eraction 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 Ph ysics. [S0021-9606(99)50115-3].