Structural studies on gel emulsions

Abstract

Kinetically stable, optically transparent water-in-oil (W/O) high-internal-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 of two isotropic liquid phases: The dispersed phase is composed of aqueous droplets, and the continuous phase is a W/O microemulsion. The properties of the continuous phase, as well as information on droplet size in highly concentrated emulsions, are aspects of the utmost importance from both theoretical and practical points of view. In this context, the influence of temperature, oil-to-surfactant ratio, phase ratio and 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 diffusion of the surfactant covering the emulsion droplets. Continuous phase 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 increasing dispersed phase volume fraction, temperature, oil-to-surfactant ratio and salinity. These results have been interpreted on the basis of surfactant availability and interfacial tension.