Formation of Tablet-Shaped and Ribbonlike Micelles in Mixtures of an Anionic and a Cationic Surfactant

SANS experiments demonstrate the formation of tablet-shaped micelles in aqueous mixtures of an anionic (SDS) and a cationic (DTAB) surfactant. The micelles grow in size as equimolar composition is approached at a given surfactant concentration or when the mixtures are diluted at low concentrations at a given surfactant composition. In the absence of added salt, both the width and the length of the micelles increase significantly, whereas, using 0.1 M NaBr brine as a solvent, the micelles grow dramatically in length but only very slightly in width. As a result, ribbonlike micelles as long as several thousand angstroms form in the latter case.