Lamellar structures in aqueous solutions of a dimeric surfactant

The effect of salt (KBr) additions on the behavior of the dimeric surfactant 12-2-12 (ethanediyl-1,2-bis(dodecyldimethylammonium bromide)) has been investigated using small-angle neutron scattering and electron microscopy. In the range of surfactant volume fraction 0.08-0.25 only wormlike micelles or lamellar structures are obtained depending on the temperature and the salt content. Two different bilayer structures are observed: one, metastable, which obeys the dilution law up to a maximum swelling corresponding to an intermicellar distance of similar to 220 Angstrom; the other at equilibrium with a constant swelling corresponding to an interlamellar distance of similar to 70 Angstrom. These results confirm the propensity of the gemini surfactants with a short spacer between the polar heads to form collapsed bilayers structured in stacks.