Abstract
A precision-machined cross-slot flow geometry with a shape that has been optimized by numerical simulation of the fluid kinematics is fabricated and used to measure the extensional viscosity of a dilute polymer solution. Full-field birefringence microscopy is used to monitor the evolution and growth of macromolecular anisotropy along the stagnation point streamline, and we observe the formation of a strong and uniform birefringent strand when the dimensionless flow strength exceeds a critical Weissenberg number Wicrit 0:5. Birefringence and bulk pressure drop measurements provide self consistent estimates of the planar extensional viscosity of the fluid over a wide range of deformation rates (26 s1 "_ 435 s1) and are also in close agreement with numerical simulations performed by using a finitely extensible nonlinear elastic dumbbell model.
Original language | English |
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Article number | 128301 |
Number of pages | 5 |
Journal | Physical Review Letters |
Volume | 109 |
Issue number | 12 |
DOIs | |
Publication status | Published - 17 Sept 2012 |
Keywords
- flow geometry
- microfluidics
- rheometry
- polymer solutions
- anisotropy
- birefringence
- cross-flow