Paper Number
NF13 

Session
Non-Newtonian Fluid Mechanics & Instabilities

Title
Stress-concentration coupling in polymer solutions under strong flow

Presentation Date and Time
February 15, 2017 (Wednesday) 2:20

Track / Room
Track 2 / Audubon A

Authors (Click on name to view author profile)

1. Cromer, Michael (Rochester Institute of Technology)
2. Leal, Gary (University of California Santa Barbara)
3. Fredrickson, Glenn (University of California Santa Barbara)

Author and Affiliation Lines (in printed abstract book)
Michael Cromer¹, Gary Leal², and Glenn Fredrickson^2
1Rochester Institute of Technology, Rochester, NY; ²University of California Santa Barbara, Santa Barbara, CA

Speaker / Presenter 
Cromer, Michael

Text of Abstract
A key assumption underlying many theoretical fluid mechanics studies of complex fluids is that the fluid composition remains homogeneous. Specifically, it is often assumed for polymeric solutions that the concentration of the polymer is independent of position in the rest state and remains so in the presence of flow. On the other hand, many industrial flows of complex fluids are nonhomogeneous.

In this work, we generalize the classical analysis of polymer fluctuations in shear flow to consider the same problem for general linear flows, with an emphasis on mixed (shear + extensional) flows. The theoretical foundation is that of the Helfand-Fredrickson mechanism in which polymer molecules can migrate up stress gradients, toward regions of higher concentration, hence providing a mechanism to enhance naturally occurring thermal fluctuations. We develop and apply a modernized version of the two-fluid model for highly entangled polymer solutions, which are well described by the Rolie-Poly constitutive model. The goal of this work is to use concentration fluctuation analysis to devise criteria by which one can ascertain whether being a “strong flow” is sufficient to make scattering patterns appear like a rotated version of pure extension. For the types of polymer solutions of interest to this work, our simulations reveal that scattering patterns under flows that are classified as “strong” (in which extension controls the chain dynamics) may deviate from the behavior expected under extensional flow and reveal a non-trivial influence of shear flow.