Paper Number
PG11 

Session
Polyelectrolytes, Self-assembling Systems & Gels

Title
Rheological and alignment transitions in wormlike micelle solutions

Presentation Date and Time
October 17, 2018 (Wednesday) 10:40

Track / Room
Track 3 / Bellaire

Authors (Click on name to view author profile)

1. Weston, Javen (University of Tulsa, Chemical Engineering)
2. Weigandt, Katie M. (NIST, Center for Neutron Research)
3. Hudson, Steven (NIST, Polymers and Complex Fluids Group)

Author and Affiliation Lines (in printed abstract book)
Javen Weston¹, Katie M. Weigandt², and Steven Hudson^3
1Chemical Engineering, University of Tulsa, Tulsa, OK 74104; ²Center for Neutron Research, NIST, Gaithersburg, MD 20899; ³Polymers and Complex Fluids Group, NIST, Gaithersburg, MD 20899

Speaker / Presenter 
Weston, Javen

Text of Abstract

RheoSANS experiments were used to track segmental alignment in semi-dilute wormlike micellar solutions. In these experiments a peak in segmental alignment was observed at a certain shear rate, above which a relatively sharp decrease in alignment is observed. The transition appears to be the result of an elastic instability due to the curved streamlines present in the Taylor-Couette geometry used for RheoSANS experiments. 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. Interestingly, similar peaks in segmental alignment are observed with these samples in another flow geometry; a microfluidic slit rheometer that allows for simultaneous SANS of samples 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. Temperature also strongly affects the behavior of the fluid and can be used to shift the critical shear rate where the transition occurs. Here, we present work investigating the cause of the observed transitions in fluid structure and rheology 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. Understanding the visco-elastic 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.

1) P. Pakdel and G.H. McKinley. “Elastic Instability and Curved Streamlines,” Phys. Rev. Lett. 1996. 2459-2462.
2) J.S. Weston, D.P. Seeman, D.L. Blair, P.F. Salipante, S.D. Hudson, K.M. Weigandt. “Simultaneous slit rheometry and in situ neutron scattering,” Rheo. Acta, 2018. 241-250.