Paper Number
IN7 

Session
Flow-induced Instabilities in Non-Newtonian Fluids

Title
Optimized microfluidic device for homogeneous uniaxial and biaxial elongation of mobile fluids

Presentation Date and Time
October 12, 2022 (Wednesday) 9:50

Track / Room
Track 5 / Sheraton 2

Authors (Click on name to view author profile)

  1. Haward, Simon J. (Okinawa Institute of Science and Technology)
  2. Shen, Amy Q. (Okinawa Institute of Science and Technology)
  3. Varchanis, Stylianos (Okinawa Institute of Science and Technology)
  4. Toda-Peters, Kazumi (Okinawa Institute of Science and Technology)
  5. Alves, Manuel A. (Faculdade de Engenharia da Universidade do Porto)
  6. Pimenta, Francisco (Faculdade de Engenharia da Universidade do Porto)

Author and Affiliation Lines (in printed abstract book)
Simon J. Haward1, Amy Q. Shen1, Stylianos Varchanis1, Kazumi Toda-Peters1, Manuel A. Alves2 and Francisco Pimenta2
1Okinawa Institute of Science and Technology, Okinawa, Japan; 2Faculdade de Engenharia da Universidade do Porto, Porto 4200-465, Portugal

Speaker / Presenter 
Haward, Simon J.

Keywords
experimental methods; computational methods; flow-induced instabilities; polymer solutions; rheometry techniques

Text of Abstract
The Optimized Shape Cross-slot Extensional Rheometer (OSCER) is a stagnation point microfluidic device, based on the planar cross-slot geometry, which has a numerically-optimized wall profile producing near ideal planar elongation [1,2]. In this work, a similar shape optimization strategy is employed on a ‘6-arm cross-slot’ [3,4], resulting in a three-dimensional (3D) geometry that produces almost ideal uniaxial (and biaxial) elongation. The optimal geometry is microfabricated to high precision in fused silica glass using the subtractive 3D-printing technique of selective laser-induced etching. Micro-particle image velocimetry (µ-PIV), for flow of a Newtonian glycerol/water mixed solvent that is refractive index-matched to the glass microdevice, demonstrates that the device does indeed produce the velocity profiles expected for both uniaxial and biaxial extension (depending on the direction of the imposed flow). The new device (called the Optimized Uni and Biaxial Extensional Rheometer, OUBER) is employed, along with the pre-existing OSCER device, to compare between the uniaxial, planar and biaxial extensional flow response of a range of dilute poly(acrylamide) solutions. For this, µ-PIV and pressure loss measurements are combined, revealing significant differences between the viscoelastic response (i.e., flow field perturbation, stability conditions, and apparent extensional viscosity) in each mode of extension, that may not be well predicted by current theories. [1] M. A. Alves, in Proceedings of the XVth International Congress on Rheology, edited by L. G. Leal, R. H. Colby, and A. J. Giacomin (American Institute of Physics, Monterey, 2008). [2] S. J. Haward, M. S. N. Oliveira, M. A. Alves, and G. H. McKinley, Phys. Rev. Lett. 109, 128301 (2012) [3] S. J. Haward, C. C. Hopkins, K. Toda-Peters, and A. Q. Shen, Appl. Phys. Lett. 114, 223701 (2019) [4] F. Pimenta, K. Toda-Peters, A. Q. Shen, M. A. Alves, and S. J. Haward, Exp. Fluids 61, 204 (2020)