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 . 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 () and are also in close agreement with numerical simulations performed by using a finitely extensible nonlinear elastic dumbbell model.
- Received 1 May 2012
DOI:https://doi.org/10.1103/PhysRevLett.109.128301
© 2012 American Physical Society