Paper Number
SG8 

Session
Self-assembled Systems, Gels and Liquid Crystals

Title
Static and dynamic signatures of branching in wormlike micelles (WLMs)

Presentation Date and Time
February 13, 2017 (Monday) 2:20

Track / Room
Track 3 / White Ibis

Authors (Click on name to view author profile)

1. Calabrese, Michelle A. (University of Delaware, Chemical & Biomolecular Engineering)
2. Rogers, Simon A. (University of Illinois, Urbana Champaign, Chemical & Biomolecular Engineering)
3. Porcar, Lionel (Institut Laue-Langevin, Large Scale Structures)
4. Wagner, Norman J. (University of Delaware, Chemical & Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Michelle A. Calabrese¹, Simon A. Rogers², Lionel Porcar³, and Norman J. Wagner^1
1Chemical & Biomolecular Engineering, University of Delaware, Newark, DE 19716; ²Chemical & Biomolecular Engineering, University of Illinois, Urbana Champaign, Urbana, IL; ³Large Scale Structures, Institut Laue-Langevin, Grenoble, France

Speaker / Presenter 
Calabrese, Michelle A.

Text of Abstract
Altering the topology of self-assembled surfactant solutions and chemical polymers provides a route for tailoring key properties, such as the rheology. Here, we develop an empirical understanding of the role of branching on the linear and nonlinear shear properties of worm-like micelles (WLMs). A model series of WLMs with controlled levels of branching is studied via the combination of linear and nonlinear rheology, dynamic light scattering (DLS), and advanced neutron techniques to distinguish features of branching. The degree of branching in the mixed cationic/anionic surfactant (CTAT/SDBS) system is controlled via the addition of the hydrotropic salt sodium tosylate, and is confirmed by cryo-TEM [1,2]. The linear viscoelastic rheology (LVE) shows deviations from Maxwellian behavior with branching, and the spectra are connected to two distinct relaxation modes identified by DLS and neutron spin echo (NSE). Orthogonal superposition rheology (OSP) is used to quantify the changes in the LVE spectra under shear, which are distinct for different branching levels. The normalized orthogonal plateau modulus, G0, and crossover frequency as a function of Wi decrease more rapidly with branching, indicating a breakdown of network-like structures. Shear startup measurements indicate that branching inhibits shear banding, as well as the stress overshoot, which has been observed in polymeric systems of different topologies [3]. The disappearance of shear banding with branching is confirmed with time- and spatially-resolved flow-small angle neutron scattering (flow-SANS) measurements in two shear planes. This research employs advanced rheological and neutron techniques to determine characteristic differences in linear versus branched WLMs, and is part of a broader effort to characterize branching in chemical polymers and self-assembled systems.

[1] Schubert, B., N.J. Wagner, and E.W. Kaler, Langmuir 19(10): 2003. [2] Calabrese, M.A., et al., J Rheol 59(5): 2015. [3] Snijkers, F., et al., J Rheol 57(4): 2013.