Paper Number
IN11
Session
Flow Induced Instabilities and Non-Newtonian Fluids
Title
High Weissenberg number flow alignment transitions in wormlike micelles
Presentation Date and Time
October 21, 2019 (Monday) 4:10
Track / Room
Track 4 / Room 305B
Authors
- Weston, Javen (University of Tulsa, Chemical Engineering)
- Weigandt, Katie M. (NIST Center for Neutron Research)
- Hudson, Steven (NIST)
Author and Affiliation Lines
Javen Weston1, Katie M. Weigandt2, and Steven Hudson3
1Chemical Engineering, University of Tulsa, Tulsa, OK 74104; 2NIST Center for Neutron Research, Gaithersburg, MD 20877; 3NIST, Gaithersburg, MD 20899
Speaker / Presenter
Weston, Javen
Text of Abstract
Simultaneous rheological measurements and Small Angle Neutron Scattering experiments were used to track segmental alignment in semi-dilute wormlike micellar solutions. As would be expected, noticeable segmental alignment begins to occur at Wi ˜ 1 for all tested solutions However, the alignment behavior deviates greatly from sample to sample at higher Wi. Additionally, all of the samples exhibit a peak in segmental alignment at some critical shear rate, above which a sometimes sharp decrease in alignment is observed. The transition appears to be the result of an elastic instability resulting from the curved streamlines present in the Taylor-Couette geometry, but is also affected by the microstructural properties of the micellar solutions. The phenomenon was investigated using a variety of sample geometries and the alignment transition was seen to follow the Pakdel-Mckinley criterion predicting flow instability for viscoelastic fluids. Here, we present work attempting to tie the microstructural properties of the micellar solutions directly to the observed high-Wi transitions in segmental alignment and apparent viscosity. and how various factors affect that transition in order to provide insight into the structure-property relationship in the high shear rate regime for this commercially-relevant system. We also present results showing similar peaks in segmental alignment observed in a microfluidic slit rheometer where the samples are undergoing Poiseuille flow. In this flow cell a peak in alignment is observed in the near-wall region of the slit where the maximum shear rate is observed. Understanding the viscoelastic properties and flow-induced structure of these micelles is beneficial for their use in personal care, oil recovery, and other applications. The system studied here is a useful model, since the micelle alignment is relatively easy to interpret and the formulation is similar to commercial consumer cleansers.