J. Phys. II France
Volume 5, Numéro 5, May 1995
Page(s) 657 - 664
DOI: 10.1051/jp2:1995155
J. Phys. II France 5 (1995) 657-664

Bilayers Versus Micelles in Very Dilute Surfactant Ternary Systems

M. Filali, J. Appell and G. Porte

Groupe de Dynamique des Phases Condensées UA 233 du CNRS, Case 026, Université Montpellier II, 34095 Montpellier Cedex 05, France

(Received 19 December 1994, revised 25 February 1995, accepted 16 March 1995)

Using neutron scattering, we investigate the structure at local scale of very dilute solutions of a quasiternary surfactant system. For such systems consisting of surfactant and cosurfactant in brine, a critical line is often found in the very dilute range of the phase diagram where the L3 sponge domain is continuously connected to the micellar domain. Our purpose is to examine the evolution of the morphology of the surfactant aggregates close to this critical line. Starting in the L3 sponge domain and approaching the transition line, we find that the neutron scattering patterns deviate more and more from that of an infinite bilayer. Furthermore, far away on the other side of the critical line, the neutron scattering patterns reveal that the initial bilayers have been replaced by long 1D cylindrical micelles. These findings are discussed in terms of the two different mechanisms that have been considered in the literature as being possibly at the origin of the critical behaviour: the symmetry breaking of the sponge and the spontaneous tearing of the bilayer.

© Les Editions de Physique 1995