Paper Number
IN34
Session
Flow Induced Instabilities and Non-Newtonian Fluids
Title
Non-homogeneous flows in entangled polymer solutions driven by flow-concentration coupling
Presentation Date and Time
October 23, 2019 (Wednesday) 1:30
Track / Room
Track 4 / Room 305B
Authors
- Burroughs, Michael C. (University of California, Santa Barbara, Chemical Engineering)
- Helgeson, Matthew E. (University of California, Santa Barbara, Chemical Engineering)
- Leal, L. Gary (University of California, Santa Barbara, Chemical Engineering)
Author and Affiliation Lines
Michael C. Burroughs, Matthew E. Helgeson, and L. Gary Leal
Chemical Engineering, University of California, Santa Barbara, Santa Barbara, CA 93101
Speaker / Presenter
Burroughs, Michael C.
Text of Abstract
Models for entangled polymer solutions often assume that both the flow and fluid composition remain uniform during shearing. However, it is well-known that a coupling of viscoelastic and osmotic stresses drives flow-enhanced concentration fluctuations, which violates the uniformity of the fluid composition. A natural question is thus whether and how such concentration fluctuations can modify the underlying flow of the material. To address this, we study solutions of polystyrene and polybutadiene in a marginal solvent as a model system in which the osmotic compressibility, and therefore the degree of flow-concentration coupling, is varied with temperature. Simultaneous rheology, velocimetry, and microscopy measurements reveal a wealth of non-homogeneous flow behavior which occurs in systems exhibiting flow-induced heterogeneities in concentration. In some systems, flow-concentration coupling produces flow-enhanced local concentration fluctuations that drive a dramatic transient shear banding, in which the local shear rates within bands strongly oppose the geometrically imposed stress gradient. In other systems, steady state shear banding is observed that qualitatively resembles that found in other reports of shear banding in highly entangled polymer solutions. These experimental results are compared to the predictions of a recently developed two-fluid model that accounts for flow-concentration coupling with the Rolie-Poly constitutive equation. The results suggest significant departures from homogeneous flow can occur in highly entangled polymer solutions due to both local and nonlocal heterogeneities in concentration.