Paper Number
SF18 

Session
Surfactants, Foams, and Emulsions

Title
Scaling of flow-induced alignment and the possibility of flow-induced scission in wormlike micelles

Presentation Date and Time
October 22, 2019 (Tuesday) 11:05

Track / Room
Track 5 / Room 306A

Authors (Click on name to view author profile)

1. Zhang, Jiamin (University of California, Santa Barbara, Chemical Engineering)
2. Leal, L. Gary (University of California, Santa Barbara, Chemical Engineering)
3. Helgeson, Matthew E. (University of California, Santa Barbara, Chemical Engineering)

Author and Affiliation Lines (in printed abstract book)
Jiamin Zhang, L. Gary Leal, and Matthew E. Helgeson
Chemical Engineering, University of California, Santa Barbara, Santa Barbara, CA 93106

Speaker / Presenter 
Zhang, Jiamin

Text of Abstract
Wormlike micelles (WLMs) are ubiquitous in consumer products and oilfield applications, and have rheology similar to that of entangled polymer solutions. Although there have been considerable experimental and theoretical studies of the rheology of WLMs, there are still relatively few models for their rheology that incorporate the physics of reversible chain scission and recombination that distinguishes WLMs from polymers. In particular, it is still unknown how flow affects the scission and recombination process and the resulting length distribution of the micelles. Although flow-small angle neutron scattering (flow-SANS) is suitable for characterizing the effects of flow on micelle length distribution, previous flow-SANS studies of WLMs were complicated by micelle branching as well as flow instabilities such as shear banding and elastic instability. To circumvent these issues, we report flow-SANS experiments on a series of linear, weakly entangled WLMs, and focus measurements on stable flows before the onset of elastic instability. These measurements are used to characterize flow-induced alignment and changes in micelle length distribution. We find that, for fixed micelle concentration, the degree of micellar alignment is determined only by the Weissenberg number, regardless of the equilibrium length distribution of micelles, which we modulate through changes in temperature. We test whether the observed power law scaling of micellar alignment with Weissenberg number can be predicted from constitutive models commonly used for WLMs. Furthermore, we use simulations of scattering from rod-like objects in shear flow in order to deconvolute the contributions to the scattering due to changes in micelle orientation from effects due to changes in micelle structure in flow. These comparisons are used to provide an outlook for whether the length distribution of wormlike micelles is significantly affected by flow.