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