Relaxation of fibrils in blends with one viscoelastic component: Bulk and confined conditions

Using a counter rotating parallel plate shear flow cell, shape relaxation of fibrils in a quiescent matrix is studied microscopically. Both the effects of geometrical confinement and component viscoelasticity are systematically explored. By applying a supercritical shear flow for varying amounts of time, droplets with a wide range of initial elongation ratios have been generated. The shape relaxation of these elongated droplets occurs in two stages; the first one consists of shape changes and retraction from a fibril to an ellipsoid, the second one is the retraction of this ellipsoid to a sphere. During both stages of the relaxation process, droplet viscoelasticity has no influence on the relaxation, whereas matrix viscoelasticity and geometrical confinement result in a slower retraction. However, the effect of confinement on the shape relaxation during the first stage of the relaxation process is less pronounced than its influence on the retraction of ellipsoidal droplets. The relaxation time of the second stage of the relaxation corresponds to the relaxation time of initially ellipsoidal droplets. Finally, for confinement ratios up to 0.75 and Deborah numbers around 1, no effect of confinement and component viscoelasticity on the critical initial elongation ratio for breakup during relaxation has been foun