BILAYERS VERSUS MICELLES IN VERY DILUTE SURFACTANT TERNARY-SYSTEMS

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 critica l line is often found in the very dilute range of the phase diagram wh ere the L3 sponge domain is continuously connected to the micellar dom ain. 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 ne utron scattering patterns deviate more and more from that of an infini te bilayer. Furthermore, far away on the other side of the critical li ne, the neutron scattering patterns reveal that the initial bilayers h ave been replaced by long 1D cylindrical micelles. These findings are discussed in terms of the two different mechanisms that have been cons idered in the literature as being possibly at the origin of the critic al behaviour: the symmetry breaking of the sponge and the spontaneous tearing of the bilayer.