Paper Number
PS10
Session
Polymers in Solution
Title
Nonhomogeneous flows during startup shear of highly entangled polystyrene solutions
Presentation Date and Time
October 15, 2018 (Monday) 3:45
Track / Room
Track 4 / Post Oak
Authors
- Burroughs, Michael C. (University of California, Santa Barbara, Chemical Engineering)
- Helgeson, Matthew E. (University of California, Santa Barbara)
- Leal, L. Gary (University of California, Santa Barbara)
Author and Affiliation Lines
Michael C. Burroughs, Matthew E. Helgeson, and L. Gary Leal
Chemical Engineering, University of California, Santa Barbara, Santa Barbara, CA 93106
Speaker / Presenter
Burroughs, Michael C.
Text of Abstract
Constitutive models for entangled polymer solutions have received continual refinement to incorporate the mechanisms of reptation, chain stretch, convective and reptation-based constraint release, and contour length fluctuations. The success of these models is commonly assessed by the ability to fit rheological data. However, increasing experimental evidence suggests that the effect of constitutive behavior on flow is an important consideration for further model development. Here, we present new experimental evidence from simultaneous rheological and particle tracking velocimetry (rheo-PTV) measurements in Taylor-Couette flow of anomalous flow in startup of steady shear of entangled solutions of polystyrene in dioctyl phthalate with otherwise expected rheological behavior. Specifically, we find reasonable agreement in measured rheology under steady shear compared to Rolie-Poly constitutive model predictions for solutions with varying entanglement number, Z. For low Z, predictions of the Rolie-Poly model are also in agreement with transient shear stress and flow velocimetry data. However, for Z > 30, strong departure from the Rolie-Poly predictions of the flow kinematics are observed. Interestingly, we find steady state velocity profiles that resemble shear banding, with gradients in shear rate that oppose the inherent stress gradient of Taylor-Couette flow. PTV measurements of the transient response of these solutions' flow kinematics under startup of steady shear provides a potential explanation for this previously unobserved and unpredicted behavior. Overall, the results indicate that monotonic constitutive behavior does not preclude the possibility of nonhomogeneous flow of polymer solutions, and highlights the importance of simultaneous flow visualization and rheological measurement to test rheological models for entangled polymer solutions under nonlinear flows.