Purely elastic instabilities in a microfluidic flow focusing device

In this work, we investigate the behavior of dilute and semidilute polymer solutions flowing in a microfluidic flow focusing device, in which an inlet stream is stretched by two balanced lateral streams. By varying the flow rates in the inlet and lateral channels and their ratio, several types of flow transitions are observed and the resulting velocity fields are analyzed both upstream and downstream of the intersection. At high flow rates, the flow becomes chaotic and the path to this state depends on both the Weissenberg number and the imposed Hencky strain. The thresholds of successive elastic instabilities leading to the chaotic state are also investigated using time-resolved microparticle imaging velocimetry.