TRANSIENT RHEOLOGICAL RESPONSE AND MORPHOLOGY EVOLUTION OF IMMISCIBLEPOLYMER BLENDS

The response of semi-concentrated model blends (10% disperse phase), c onsisting of slightly viscoelastic polymers, on a stepwise increase in shear rate is investigated. During the initial stage of the response droplets deform into fibrils. The shear and normal stress transients d uring the deformation process are modeled by combining the approach of Doi and Ohta with the affine deformation theory for single droplet be haviour. In the proposed equations the scaling relations of Doi and Oh ta for transient stresses are preserved. They do not contain any fitti ng parameter. First, the model predictions are compared with experimen tal results on model blends. Good agreement is found under conditions for which affine deformation is expected. Second the applicability of the scaling relations of the Doi-Ohta theory is verified experimentall y. Although the scaling laws should only apply for 50:50 mixtures of N ewtonian liquids with equal viscosity, the experiments show that they hold as well for semiconcentrated systems containing slightly viscoela stic components with viscosity ratios deviating from unity. (C) 1997 T he Society of Rheology.