Bicontinuous microemulsions revisited: a new approach to freeze fracture electron microscopy (FFEM)

New images by freeze fracture electron microscopy (FFEM) are obtained for microemulsions in the ternary system water–n-octane–C12E5 as function of varying water-to-oil ratio. The surfactant concentration is chosen such that the composition of the sample is close to the X̃-point, i.e. the point of highest efficiency, where the three- and the one-phase regions meet. As the phase behavior and thus the microstructure of these particular nonionic microemulsions are extremely sensitive to temperature, a precise temperature control of the sample was necessary prior to rapid freezing in liquid ethane. The images presented are the first FFEM images along the trajectory of the middle-phase in phase space. Of particular interest is the structure of the microemulsion on the water-rich side not visualized so far. The images give strong evidence that even at the highest water and oil contents, respectively, elements of a bicontinuous microstructure are visible, which confirms results obtained by means of various other techniques.