STRUCTURE OF CUBIC MESOMORPHIC PHASES DETERMINED BY LOW-TEMPERATURE TRANSMISSION ELECTRON-MICROSCOPY AND SMALL-ANGLE X-RAY-SCATTERING

Cubic phases exist in many amphiphile/water systems at high solute concentrations between the lamellar and hexagonal phases, and at lower amphiphile concentrations between micellar and hexagonal phases. The structure of the latter is still controversial. Structural models that have been suggested to satisfy the experimental data all lacked direct evidence to prove their validity. The structural model we report here is based on a combination of direct and indirect experimental techniques. Direct imaging by low-temperature (cryo) transmission electron microscopy (TEM) of vitrified specimens provides the geometry and size of the building blocks of the phase, in this case globular micelles, and shows directly the existence of a cubic phase. The indirect method small-angle X-ray scattering (SAXS), provides the symmetry group of these cubic phases, the size of the unit cells and the positions of the 24 globular micelles in these unit cells. Beyond solving the microstructure of model cubic phases of the anionic surfactant HCO-60/water system and providing, for the first time, direct images of this cubic phase and of lysolecithin/water, we demonstrate a general approach for combining direct and indirect methods to solve microstructures of complex fluids. © 1990 American Chemical Society.