3096
Langmuir 1997, 13, 3096-3102
Phase Behavior of Aqueous Solutions of a Dimeric Surfactant E. Buhler,† E. Mendes,† P. Boltenhagen,† J. P. Munch,† R. Zana,‡ and S. J. Candau*,† Laboratoire d’Ultrasons et de Dynamique des Fluides Complexes, Unite´ de Recherche Associe´ e au CNRS No. 851, Universite´ Louis Pasteur, 4, rue Blaise Pascal, 67070 Strasbourg Cedex, France, and Institut Charles Sadron (CRM-EAHP), 6, rue Boussingault, 67083 Strasbourg Cedex, France Received November 13, 1996. In Final Form: March 17, 1997X The effect of salt (KBr) additions on the behavior of the dimeric surfactant 12-2-12 (ethanediyl-1,2bis(dodecyldimethylammonium bromide)) has been investigated using small angle neutron scattering (SANS) and dynamic light scattering (DLS). The effect of temperature and additions of DTAB (dodecyltrimethylammonium bromide, “monomer” of 12-2-12) has also been investigated. Upon increasing salt content, the partial phase diagram of the water/salt/12-2-12 system shows the sequence wormlike micelle phase, lamellar phase, and biphasic systems with a salt-rich, surfactant-poor lower phase and a salt-poor lamellar upper phase. This study is the first one reporting a salt-induced transition between a wormlike micelle phase and a lamellar phase. Additions of DTAB at low mole fraction (
