The symmetric-asymmetric transition of the sponge phase : I. Effect of the salinity

A systematic study of pseudotemary systems made of salted water, pentanol and SDS is presented for salt concentrations ranging from 20 to 80 g/l of Nacl. In the dilute part of the phase diagram, the system with the lowest salt concentration is known to present a continuous phase transition between phases of randomly interconnected membranes, namely a sponge (symmetric) and an asymmetric phase, The same topology is found as the salt concentration is increased and the evolution of the characteristics of the symmetric-asymmetric phase transition is studied. Light JOURNAL DE PHYSIQUE II T 4 N'7 JULh lW4 l166 JOURNAL DE PHYSIQUE II N° 7 scattering experiments are first described. We show that the scattered intensity should be analysed in terms of a product of a structure and a form factor. The latter contribution gives directly the geometrical size of the phase (the mean distance between the membranes) without using