Morphology development during phase inversion of a PS/PE blend in isothermal, steady shear flow

Abstract

The morphological changes occurring during the phase inversion of a polystyrene/polyethylene blend subjected to isothermal, steady shear flow are investigated and characterized. The isothermal, steady shear flow field provides a well-defined thermal and flow history. This contrasts with previous work on phase inversion, which was conducted in complex flow fields with large temperature gradients. The well-defined flow field permits a more detailed examination of the sequence of morphological changes during phase inversion than was accomplished previously. Both components are observed to initially deform into a sheet morphology. At strains of 200–780, the (initially continuous) minor component begins to break up, allowing the (initially dispersed) major component to coalesce. The blend becomes co-continuous around strains of 330–1500. At strains of 500–2000, the major component continues coalescing. The minor component breaks up into fibers and drops at strains of 800–3000. Breakup of the minor-component sheets is not observed until the sheets are less than 1 μm thick. Deformation and breakup of the initially dispersed phase is observed in this shear flow field, despite a viscosity ratio in excess of 10. For the system studied here, phase inversion does not occur under no-flow conditions.