Abstract
Using small angle X-ray scattering and viscosity measurements, we investigate the sponge phase changing to low dilutions of an ionic surfactant+alcohol+brine system. The scattering profiles are consistent with the elementary bilayer structure and a swelling behavior is observed over a very wide range of dilution. According to two dilution laws proposed for symmetric sponge phase, of rigid or flexible membrane, we show that the topological factor decreases in the range of low dilutions. So, the viscosity deviates from its linear variation characterizing the dilute sponge phase and it increases exponentially with the membrane volume fraction. We suggest this fluidity behavior to be related to the change of the sponge phase topological factor.