(412b) Flow of Wormlike Micellar Fluids Around a Sharp Microfluidic Bend: Effects of Branching and Shear-Banding

The flow of wormlike micellar solutions around a 90° sharp microfluidic bend was studied using rheometry, flow visualization, and velocimetry. By carefully choosing the test solution composition, all four combinations of linear or branched micelles and shear-banding or non-shear-banding solutions were accessed using four wormlike micellar solutions of CpCl/NaSal. The flow behavior of the solutions was examined over similar conditions of about 1 < Wi < 300 and 10^-6 < Re < 10^-2. When comparing the flow around the microbend of the two shear-banding solutions with the two non-shear-banding ones, the secondary flows showed distinct differences at about 10< Wi <100. Flow visualization showed that a steady lip vortex formed at the inner upstream corner of the microbend in the non-shear-banding solutions, while a lip (inner upstream corner) vortex and an outer corner vortex formed in the shear-banding solutions. On the other hand, when comparing the solutions with similar rheological characteristics but different micelle morphology (linear versus branched), no significant differences in the flow behavior were observed. These results suggest that shear-banding plays a central role in determining the secondary flow behavior around the microbend, while the effect of micelle morphology is minimal for wormlike micelle solutions.