Aggregation Phenomena in Water-in-Oil Emulsions

We report the phase behavior of monodisperse water-in-oil emulsion droplets. We show that depending upon the droplet size, the surfactant concentration within the continuous oil phase, the chemical nature of the oil, and the temperature, the emulsion droplets may remain dispersed or reversibly aggregated. Close to the phase transition threshold, we observe coexisting phases, whereas much above, we preferentially observe gels. Since such phase transitions exhibit the same trends than what was previously observed in direct oil-in-water emulsions, a size purification process based on the same principles is accessible in the coexisting regime. We present phase diagrams for two different droplet sizes that describe the main qualitative features of these systems.