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

The morphological changes occurring during the phase inversion of a polysty rene/polyethylene blend subjected to isothermal, steady shear flow are inve stigated and characterized. The isothermal, steady shear flow field provide s a well-defined thermal and flow history. This contrasts with previous wor k 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 inversio n than was accomplished previously. Both components are observed to initial ly deform into a sheet morphology. At strains of 200-780, the (initially co ntinuous) minor component begins to break up, allowing the (initially dispe rsed) major component to coalesce. The blend becomes co-continuous around s trains of 330-1500. At strains of 500-2000, the major component continues c oalescing. The minor component breaks up into fibers and drops at strains o f 800-3000. Breakup of the minor-component sheets is not observed until the sheets are less than 1 mu m thick. Deformation and breakup of the initiall y 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 n ot occur under no-flow conditions. (C) 1999 Elsevier Science Ltd. All right s reserved.