WATER TRANSFER IN MIXED WATER-IN-OIL EMULSIONS STUDIED BY DIFFERENTIAL SCANNING CALORIMETRY

Water transfers are observed within complex systems containing aqueous phases separated by a membrane or an oil phase, such as biological ce lls or multiple emulsions. In order to better understand water transfe r mechanism, a system made of a mixed water-in-oil (W/O) emulsion cont aining two kinds of aqueous droplets pure water and a 30 % urea soluti on - was developed. Water transfer from pure water droplets to urea so lution droplets was evidenced by Differential Scanning Calorimetry (DS C). Finally the mixed emulsion contains one kind of droplets made of a diluted urea solution which composition is in agreement with formulat ion and data obtained from experiments performed on single W/O emusion s which dispersed phase is a diluted urea solution of the same composi tion. These mixed emulsions have been pictured as a three-fluid phases system containing two aqueous phases separated by a plane oil membran e. From a homogeneous solubility diffusion model applied to a quasi-st ationnary regime, the water intra-diffusion coefficient has been obtai ned and compared to the value calculated from the Stokes-Einstein equa tion. A factor ten makes the discrepancy between the two values, the v alue deduced from the model being the highest. A possible influence of the emulsifier molecules has been evoked.