Evolution of CTAB/NaSal Micelles: Structural Analysis by SANS

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.