Anisotropic viscoelasticity and molecular diffusion in nematic wormlike micelles

ABSTRACT

Using rheo-NMR, pulsed-field-gradient NMR diffusometry and solution rheology, we observe temperature- and composition-dependent orientational order as well as director dynamics and molecular transport in a nematic wormlike micelle (WLM) system composed of cetyltrimethylammonium bromide in D₂O. We measure, for the first time over a comprehensive nematic range in WLMs, four of the five independent anisotropic viscosities by fitting nonlinear rheo-NMR director realignment data and comparing with traditional solution rheology measurements. Additionally, we extract self-diffusion coefficients in three orthogonal directions for the aligned WLM unimers as well as for the D₂O solvent molecules. Continued study and enhanced understanding of complex fluid dynamics in these anisotropic shear-modulated fluid systems can lead to advances in lubricants, coatings, oil extraction, drug delivery and tissue engineering.

GRAPHICAL ABSTRACT

KEYWORDS:

• Leslie viscosities
• rheo-NMR
• deuterium NMR
• diffusion
• rheology
• director dynamics

Acknowledgements

The authors gratefully acknowledge Rui-Chao Zhang for assistance with data collection and Xiaolin Zhang for assistance with computer software for director dynamics fits, as employed in reference [29].

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the US National Science Foundation (NSF) under Award CBET 1437767, and by the U.S. Army Research Office under Grant W911NF-07-1-0452 Ionic Liquids in Electro-Active Devices (ILEAD) MURI.