Phase deformation under shear in an immiscible polymer blend: Influence of strong permanent elastic properties

The influence of a strong permanent elasticity on droplet deformation is studied. Deformation under shear of a crosslinked dispersed copolymer of ethylene and vinyl acetate (EVA) in a poly (dimethylsiloxane) matrix was investigated using a hot optical shear device. In the first part of this work, deformation of reactive EVA droplets at different extents of crosslinking under isothermal temperature was studied in order to better understand the system. As expected, droplet deformation decreases with increasing crosslinking level. However, even when the droplets are crosslinked beyond the gel point, they continue to deform. Following this, the control of dispersed phase morphology under shear flow using the extent of crosslinking of the dispersed phase was also studied. Fixed fibrillar morphology can be obtained by adjusting the shear rate so that crosslinking reaction occurs before the breakup of the EVA fibers. In the same way, fixed nodular morphology can be generated if fiber relaxation occurs before the crosslinking level becomes too high. Depending on the shear rate needed to generate fibers, the final nodular morphology obtained can be coarse or fine. (C) 2004 The Society of Rheolog