Paper Number
SF19
Session
Surfactants, Foams, and Emulsions
Title
Probing topological transitions of reverse worm-like micelles subject to transient shear flow using dielectric spectroscopy
Presentation Date and Time
October 22, 2019 (Tuesday) 11:30
Track / Room
Track 5 / Room 306A
Authors
- Richards, Jeffrey J. (Northwestern University, Chemical & Biological Engineering)
- Cho, Noah H. (Northwestern University, Chemical & Biological Engineering)
- Riley, John K. (National Institute of Standards and Technology, Center for Neutron Research)
Author and Affiliation Lines
Jeffrey J. Richards1, Noah H. Cho1, and John K. Riley2
1Chemical & Biological Engineering, Northwestern University, Evanston, IL 60208; 2Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899
Speaker / Presenter
Cho, Noah H.
Text of Abstract
Worm-like micelles (WLMs) are ubiquitous in industrial materials. WLMs exhibit unique dynamics due to their self-assembled structure that permits the chains to break and reform. These dynamics contribute to a rich and not well-understood microstructural behavior in response to deformation. Recent work has focused on the important role that linear and branched worm topology plays in the approach to non-linearity and on the onset of shear-banding in steady and transient flows. While linear to branched topological transitions in aqueous worm-like micelles are commonly induced through the addition of salt, questions remain about the role that electrostatic interactions play in determining the onset of shear banding and dynamics shear banding. We have recently used dielectric rheology to study the transition from linear to branched WLMs using inverse microemulsion system formed from lecithin/water/decane. A topological transition from linear to branched WLMs occurs as water is added to the microemulsions and is marked by a maximum in the zero-shear viscosity. Due to the nonpolar nature of decane, this system enables the use of dielectric measurements to distinguish between the segmental chain and branch-breaking/formation dynamics during Rheo-dielectric measurements in steady shear. Combined with in situ small angle neutron scattering, we found that shear-induced alignment of branched WLMs is preceded by the breaking of branch points that contributes to the stress-dissipation and is marked by a distinct increase in the low-frequency permittivity. This behavior was distinct from that observed in linear WLMs. We report the extension of this approach to study transient flows, including large-amplitude oscillatory shear, start-up and cessation experiments. The additional contributions of the branch breaking mechanism on the primary relaxation process will be presented in terms of the dielectric, the rheological responses, and the alignment-driven anisotropy under the transient shear flow.