PHASE-BEHAVIOR AND SCATTERING OF DOUBLE-CHAIN SURFACTANTS IN DILUTED AQUEOUS-SOLUTIONS

The binary phase diagram of two typical double chain cationic surfactantss is studied in the diluted regime. From scattering studies in the four microstructures seen, it is shown that the binodal tie lines of the swollen lamellar liquid to isotropic transition are hidden by a metastable L3 phase and a biphasic dispersion of spherulitic crystallites. The maximum swelling in biphasic systems is studied in the presence of added salt and it is shown that maximum swelling distance between bilayers is not set by equilibrium between attractive and repulsive forces but by equilibrium of osmotic pressures of water in the two coexisting phases.