A section of t h e composition-temperature phase prism of a ternary non-ionic surfactant-water-oil system defined by a constant surfactant to oil ratio has been investigated. The structural sequence of normal spheres to planar bilayers, via cylinders, is observed a s a function of decreasing water concentration at fixed temperature.As a function of increasing temperature at fixed surfactant and oil concentration, we note the commonly observed reversal in mean curvature of the polar/apolar interface. The mean curvature progressively alters from positive values in t h e low-temperature microemulsion phase to negative mean curvature in t h e hightemperature L, phase, with an intermediate lamellar phase where t h e mean curvature passes through zero. The phase diagram of this section is similar to that of, the binary surfactant-water system. The average area per surfactant at the polar/apolar interface is 46 & 2 A2. A micellar cubic phase is observed between t h e microemulsion and the hexagonal phase while no bicontinuous cubic phase is observed.

We have investigated a section through the composition-temperature phase prism of a ternary nonionic surfactantw a t e r 4 1 system defined by a constant surfactant to water ratio. The structural sequence normal cylindersmultiply connected bilayer-planar bilayer-reverse monolayer structure is obtained when increasing the temperature. This sequence corresponds to a gradual reversal of the mean curvature of the polar-apolar interface as the temperature is increased as has been observed previously in the corresponding microemulsion systems. The cylinders can incorporate (swell with) moderate amounts of oil. In addition to the bicontinuous cubic phase present in the binary water-surfactant system the ternary system contains a bicontinuous cubic phase with simultaneously high contents of water and oil. Upon dilution with oil, this phase undergoes an order4isorder transition to a liquid "sponge phase" (L4) retaining the multiply connected bilayer structure. A lamellar phase swells with large amounts of oil. From the variation of the periodicity with oil content we obtain the solubility of the nonionic surfactant in the oil.

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The structures of the phases formed in excess buffer (at pH 7.4) by a homologous series of saturated diacylphosphatidylethanolamines in which the headgroup is N-derivatized with biotin have been investigated for chain lengths of C(12:0) to C(20:0), using both 31P nuclear magnetic resonance (NMR) spectroscopy and small-angle X-ray diffraction. In 1 M NaCl, all lipids display 31P NMR spectra characteristic of a lamellar gel phase at low temperature. In the fluid phase, the lipids of C(12:0) and C(14:0) chain lengths display isotropic 31P NMR spectra, corresponding to aggregated phases with high surface curvature, whereas those with C(18:0) and C(20:0) chain lengths display sharp axial powder patterns characteristic of a lamellar (L alpha) phase. The lipid of intermediate C(16:0) chain length displays a more complex temperature dependence of the 31P NMR spectra in the fluid phase. The spectra convert from an axial powder pattern of unusually low chemical shift anisotropy to one characteristic of a fluid lamellar (L alpha) phase with increasing temperature. The small-angle X-ray diffraction patterns of the lipids in 1 M NaCl have lamellar repeat spacings in the gel phase which increase linearly with chain length and are consistently lower than those in the fluid phase [for chain lengths of C(16:0) to C(20:0)]. In addition, the gradient in long spacing with chain length in the gel phase is approximately half that expected for a gel phase with untilted, all-trans chains, indicating that the lipid chains are interdigitated in the gel phase (L beta i).(ABSTRACT TRUNCATED AT 250 WORDS)