Microstructure and rheology of a flow-induced structured phase in wormlike micellar solutions

Joshua J. Cardiel, Alice C. Dohnalkova, Neville Dubash, Ya Zhao, Perry Cheung, Amy Q. Shen

Research output: Contribution to journalArticle

56 Scopus citations

Abstract

Surfactant molecules can self-assemble into various morphologies under proper combinations of ionic strength, temperature, and flow conditions. At equilibrium, wormlike micelles can transition from entangled to branched and multiconnected structures with increasing salt concentration. Under certain flow conditions, micellar structural transitions follow different trajectories. In this work, we consider the flow of two semidilute wormlike micellar solutions through microposts, focusing on their microstructural and rheological evolutions. Both solutions contain cetyltrimethylammonium bromide and sodium salicylate. One is weakly viscoelastic and shear thickening, whereas the other is strongly viscoelastic and shear thinning. When subjected to strain rates of ∼103 s-1 and strains of ∼103, we observe the formation of a stable flow-induced structured phase (FISP), with entangled, branched, and multiconnected micellar bundles, as evidenced by electron microscopy. The high stretching and flow alignment in the microposts enhance the flexibility and lower the bending modulus of the wormlike micelles. As flexible micelles flow through the microposts, it becomes energetically favorable to minimize the number of end caps while concurrently promoting the formation of cross-links. The presence of spatial confinement and extensional flow also enhances entropic fluctuations, lowering the energy barrier between states, thus increasing transition frequencies between states and enabling FISP formation. Whereas the rheological properties (zero-shear viscosity, plateau modulus, and stress relaxation time) of the shear-thickening precursor are smaller than those of the FISP, those of the shear-thinning precursor are several times larger than those of the FISP. This rheological property variation stems from differences in the structural evolution from the precursor to the FISP.

Original languageEnglish (US)
Pages (from-to)E1653-E1660
JournalProceedings of the National Academy of Sciences of the United States of America
Volume110
Issue number18
DOIs
StatePublished - Apr 30 2013

Keywords

  • Mesh size
  • Microfluidics
  • Microrheology

ASJC Scopus subject areas

  • General

Fingerprint Dive into the research topics of 'Microstructure and rheology of a flow-induced structured phase in wormlike micellar solutions'. Together they form a unique fingerprint.

Cite this