STUDY OF STATE TRANSITIONS WITHIN MULTIPLE W/O/W EMULSIONS USING CALORIMETRY (DSC)

We report results obtained by differential scanning calorimetry of multiple water-oil-water emulsions. Samples were submitted to cooling (-2-degrees-C min-1) between +20 and -60-degrees-C. DSC curves showed liquid/solid transitions of both dispersed and continuous aqueous phases at subzero temperatures due to undercooling phenomena. The mean freezing temperatures found were around -15-degrees-C for the continuous aqueous phase and around -44-degrees-C for the dispersed phase. Oil did not crystallize over the temperature range studied. Furthermore, during the cooling of a multiple emulsion sample we observed a transfer of water from the internal to the external frozen aqueous phase. This transfer was attributed to the difference of vapor pressures between ice and undercooled water at the same temperature. The influence of urea, solubilized in the dispersed aqueous phase, on the observed phenomena was also studied. An evolution of the mean freezing temperature of the dispersed water was observed, showing a water transfer from the outer to the inner aqueous phase. Additional viscosity measurements performed at room temperature confirmed the occurrence of a mass transfer within the diluted multiple emulsion.