Kinetically stable, optically transparent water-in-oil (W/O) high-inte
rnal-phase-ratio emulsions with a gel-like appearance have been formed
in either hydrogenated or fluorinated water-non-ionic surfactant-oil
systems. Systematic studies undertaken to characterize these emulsions
have revealed that they form above the hydrophilic-lipophilic balance
(HLB) temperature of the corresponding ternary system. They consist o
f two isotropic liquid phases: the dispersed phase is composed of aque
ous droplets, and the continuous phase is a W/O microemulsion. The pro
perties of the continuous phase, as well as information on droplet siz
e in highly concentrated emulsions, are aspects of the utmost importan
ce from both theoretical and practical points of view. In this context
, the influence of temperature, oil-to-surfactant ratio, phase ratio a
nd salinity has been studied by videomicroscopy and small-angle X-ray
scattering (SAXS) techniques. The SAXS spectra have been explained by
the superposition of two spectra, one corresponding to the continuous
phase (W/O microemulsion peak) and the other corresponding to the diff
usion of the surfactant covering the emulsion droplets. Continuous pha
se spectra suggested that no significant differences exist between the
structures of the microemulsion under equilibrium and non-equilibrium
(i.e. gel emulsion) conditions. The droplet size increases with incre
asing dispersed phase volume fraction, temperature, oil-to-surfactant
ratio and salinity. These results have been interpreted on the basis o
f surfactant availability and interfacial tension.