Structural properties of the evolution of CTAB/NaSal micelles investigated by SANS and rheometry

Christopher N. Lam, Changwoo Do, Yangyang Wang, Guan Rong Huang, Wei Ren Chen

Research output: Contribution to journalArticlepeer-review

21 Scopus citations

Abstract

Surfactants are amphiphilic molecules that spontaneously self-assemble in aqueous solution into various ordered and disordered phases. Under certain conditions, one-dimensional structures in the form of long, flexible wormlike micelles can develop. Cetyltrimethylammonium bromide (CTAB) is one of the most widely studied surfactants, and in the presence of sodium salicylate (NaSal), wormlike micelles can form at very dilute concentrations of surfactant. We carry out a systematic study of the structures of CTAB/NaSal over a surfactant concentration range of 2.5-15 mM and at salt-to-surfactant molar ratios of 0.5-10. Using small-angle neutron scattering (SANS), we qualitatively and quantitatively characterize the equilibrium structures of CTAB/NaSal, mapping the phase behavior of CTAB/NaSal at low concentrations within the region of phase space where nascent wormlike micelles transition into long and entangled structures. Complementary rheological assessments not only demonstrate the significant influence of the inter-micellar Coulombic interaction on the micellar structure but also suggest the potential existence of a hierarchical structure which is beyond the accessibility of the SANS technique.

Original languageEnglish
Pages (from-to)18346-18351
Number of pages6
JournalPhysical Chemistry Chemical Physics
Volume21
Issue number33
DOIs
StatePublished - 2019

Funding

This research at SNS and CNMS of Oak Ridge National Laboratory was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.

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