Soft Matter Seminar: Effect of microfluidic geometry on flow instabilities of wormlike micelle solutions
Dr. Paul Salipante, NIST
The pressure driven flow of non-Newtonian fluids through pipes is common in industrial processing and high shear rate rheological measurements. Viscoelastic instabilities can complicate these measurements, especially for fluids with self-assembling microstructures such as wormlike micelle solutions. In this talk, I will focus on measurements of flow instabilities of wormlike micelle solutions in microfluidic geometries where high shear rates can be achieved at low Reynolds number. In addition to 2-D fluorescent particle image velocimetry, I will introduce advancements in using digital holographic particle tracking velocimetry to measure 3-D flow fields with high temporal resolution. This technique is used to measure velocity profiles of a jetting instability of wormlike micelle solutions in rectangular microfluidic channels. At higher flow rates, the velocity profiles are measured and compared to simultaneous slit rheology measurements, where discrepancies between the two measurements arise in channels smaller than 200 µm. I will also show results of flow behavior of wormlike micelle solutions in an axisymmetric capillary constriction, which produces a spatio-temporal instability affecting the flow throughout the fluid system. Velocimetry measurements in the entrance region show a transition to unstable flow above a critical flow rate, where large flow circulations are observed in the tapered geometry. This is further investigated using polarized light microscopy, which shows a rapid breakdown in micelle alignment at the onset of a flow spurt, indicating the importance of rapid micelle structural changes on the fluctuations.
Friday, November 30, 2018 at 10:00am to 11:00am
Regents Hall, 351
3700 O St. NW