Evolution of CTAB/NaSal Micelles: Structural Analysis by SANS

TL;DR

This study uses small-angle neutron scattering to analyze how CTAB/NaSal surfactant micelles evolve from nascent to long, entangled wormlike structures across various concentrations and molar ratios.

Contribution

It provides a detailed microscopic structural analysis of CTAB/NaSal micelles and maps their phase behavior at low concentrations, highlighting the transition to wormlike micelles.

Findings

Identification of phase transition points for micelle elongation

Quantitative characterization of micelle structures

Mapping of phase behavior at different concentrations

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 microscopic 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, 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.