Résumé
We have studied the interface between the sponge phase and the lamellar phase in different lyotropic systems. Bilayers of the lamellar phase are either tilted, or tangential to the interface. According to a current model, the situation depends on the values of the elastic constants. We have investigated the cyclohexane/ SDS/ water/ pentanol system in which the elastic constants can be changed by tuning the concentration φ of magnetic particles in cyclohexane and we have observed a transition between the two types of interface. Finally the magnetic properties have been used to estimate the very low interface tension.