RHEOLOGY AND SMALL-ANGLE NEUTRON-SCATTERING AS TOOLS FOR EVALUATING EMULSIFICATION - APPLICATION TO REVERSE HIGHLY CONCENTRATED FLUORINATEDEMULSIONS

An emulsion is a dispersion of one fluid in another nonmiscible fluid, stabilized by a surfactant. Such a mixture is not at thermodynamic eq uilibrium, and some energy is needed to create the unfavorable interfa ce. This energy is provided by a mechanical stirring. Due to the prepa ration process, the surfactant is shared among the oil/water interface (droplets surface) and the continuous phase. In this paper, we estima te the emulsification rate in relation with both the dispersed phase v olume fraction and the mechanical stirring. For low volume fraction, t his rate is very low showing that the mechanical stirring is inadequat e, whereas it becomes more efficient (but still insufficient) for high er volume fractions. Using small-angle neutron scattering under shear and rheological measurements, we follow the surfactant distribution wh en applying a steady flow: small shear flows help the aging whereas hi gh shear flows improve the fragmenting and hence the emulsification.