Droplet size evolution during coalescence in semiconcentrated model blends

The droplet-size evolution in polymer blends, due to flow-driven coalescence, is investigated 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 las 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.