SHEAR INFLUENCE ON THE PHASE-SEPARATION OF OLIGOMER BLENDS

Shear influences on the phase separation behaviour of four different b lends of ethylene glycol/propylene glycol oligomers, exhibiting upper critical solution temperatures, were investigated. Cloud point curves at rest (turbidity measurements) are reported for all systems, spinoda l conditions (light scattering) and tie-lines (analysis of the coexist ing phases) are given for some examples. Phase diagrams under shear we re obtained from rheological data. They demonstrate that the demixing temperatures of systems where both glycols bear OH end-groups are lowe red up to ca. 1-degrees-C by shear rates of 1000 s-1; the critical com position, generalized to the non-equilibrium conditions of flow, is ma rkedly shifted. These observations are explained in terms of the gener alized Gibbs energy (containing the mechanical energy the system store s during flow) as a consequence of the strongly interacting end-groups of the glycols. This interpretation is backed by the fact that the sh ear effects disappear when the glycols are methylated.