PHASE-TRANSITION BETWEEN MICROEMULSION AND LAMELLAR PHASES IN A C12E5WATER/N-OCTANE AMPHIPHILIC SYSTEM/

A ternary amphiphilic system consisting of water, n-octane and C12E5 h as been studied by small angle X-ray scattering (SAXS) to elucidate th e mechanism of phase transition between lamellar and microemulsion pha ses. SAXS profiles in the region between lamellar and microemulsion ph ases show two distinct peaks, which indicate that different structures coexist. These structures change continuously as transition goes on, which is in good agreement with the lever rule in phase diagram. The t ransition behavior has been explained as a result of the change of cur vatures of the interfacial film as a function of temperature and subse quent change of bending elastic energy. A boundary of the coexistence region is determined by the double tangent construction for the free e nergies of the microemulsion and lamellar phases.