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Numerical simulations and experimental data are compared for the investigation of the influence of viscoelasticity on drop deformation in shear. A viscoelastic drop suspended in a Newtonian liquid, or a Newtonian drop suspended in a viscoelastic liquid, is sheared and investigated for transients, relaxation after cessation of shear flow, and step‐up in shear rate. The numerical simulations are conducted at parameters chosen to model the experiments. We use the volume of fluid (VOF) continuum surface force (CSF) algorithm for situations dominated by shear. For drop relaxation experiments, we use the paraboloid representation of the interface in the surface tension force (PROST) algorithm. The Oldroyd‐B and Giesekus constitutive models are implemented. An interesting result is that by stepping up in the capillary number gradually, a stationary states is achieved at higher capillary numbers than without the graduated steps. The experimental work is described in Verhulst, Moldenaers and Cardinaels [l]. We present a summary of the numerical approach here. The reader is referred to [2] for details.

The droplet-size evolution in polymer blends, due to flow-driven coalescence, is nvestigated both experimentally and theoretically. In the experiments, preshearing at a high rate is applied to generate a fine morphology in the blend; subsequently, the shear rate is suddenly decreased to induce coalescence, and the resulting growth in droplet size is measured. It is demonstrated that rheological as well as microscopic techniques can be used for an in-situ determination of the size evolution of the droplets. Effects of shear rate, step-down ratio, and blend concentration were studied systematically. A master curve for the droplet growth at each step ratio can be obtained by plotting the relative increase in droplet diameter us. the strain after step-down in shear rate, multiplied by the fraction of the disperse-phase squared. To model the droplet-size evolution the strategy of Chesters is followed. It is implemented here for semiconcentrated blends, resulting in a one-parameter model equation that correctly describes the experimental observations.