CYLINDERS AND BILAYERS IN A TERNARY NONIONIC SURFACTANT SYSTEM

We have investigated a section through the composition-temperature pha se prism of a ternary nonionic surfactant-water-oil system defined by a constant surfactant to water ratio. The structural sequence normal c ylinders-multiply connected bilayer-planar bilayer-reverse monolayer s tructure is obtained when increasing the temperature. This sequence co rresponds to a gradual reversal of the mean curvature of the polar-apo lar interface as the temperature is increased as has been observed pre viously in the corresponding microemulsion systems. The cylinders can incorporate (swell with) moderate amounts of oil. In addition to the b icontinuous cubic phase present in the binary water-surfactant system the ternary system contains a bicontinuous cubic phase with simultaneo usly high contents of water and oil. Upon dilution with oil, this phas e undergoes an order-disorder transition to a liquid ''sponge phase' ( L4) retaining the multiply connected bilayer structure. A lamellar pha se swells with large amounts of oil. From the variation of the periodi city with oil content we obtain the solubility of the nonionic surfact ant in the oil.