Breakup of filaments in blends during simple shear flow

In this paper the breakup of droplets under shear in polymer blends is stud ied by means of linear conservative dichroism and small angle light scatter ing. More specifically breakup of long fibrils by interfacial instabilities is considered. Measurements are performed on dilute model systems containi ng nearly Newtonian components in transient flows that involve a sudden inc rease or decrease in shear rate. The experimental results are used to evalu ate the Khakhar and Ottino theory [Khakhar and Ottino (1987)]. In this theo ry breakup times are calculated starting from the onset of the instability. It is demonstrated that the scaling derived from the Khakhar and Ottino th eory also holds for the more readily accessible total breakup time, calcula ted from the onset of shear flow in a startup flow. The development of inte rfacial disturbances is studied in a flow history, which consists of genera ting fibrils by suddenly applying a shear rate followed by a sudden drop in shear rate during which the breakup process is observed. The evolution of the dominant wavelength during this process turns out to be time controlled rather than strain controlled as suggested by the theory. (C) 2000 The Soc iety of Rheology. [S0148-6055(00)00706-9].