STRUCTURE AND PHASE-BEHAVIOR OF THE TERNARY-SYSTEM WATER, N-HEPTANE AND THE NONIONIC SURFACTANT IGEPAL(R) CA520

The phase behavior of the system water, n-heptane and the nonionic sur factant Igepal(R) CA520 has been studied by visual inspection, high-pe rformance liquid chromatography, polarizing microscopy and freeze-frac ture electron microscopy. The phase diagram at 25 degrees C contains t wo large homogeneous microemulsion phases, an extended region of a lam ellar liquid crystalline structure and some two- and three-phase regio ns. The oil-rich part of the phase diagram has been investigated by st atic and dynamic light scattering in order to examine the behavior of the collective diffusion coefficient and the scattering intensity in t he presence of increasing concentrations of water, starting from the b inary system of n-heptane and Igepal(R) CA520. The results suggested t hat at a very low water content the aggregates of the microemulsion ar e small. With the exception of this region the structure is bicontinuo us.