STUDY BY DIFFERENTIAL SCANNING CALORIMETRY, RHEOMETRY AND ELECTROCONDUCTIMETRY OF MASS TRANSFERS AT SUBAMBIENT AND AMBIENT-TEMPERATURES IN MULTIPLE WATER/OIL/WATER EMULSIONS ENTRAPPING MGSO4

We have studied, at subambient and ambient temperatures, mass transfers occurring through the liquid oil membrane separating the dispersed and bulk aqueous phases of multiple water/oil/water emulsions entrapping MgSO4. This study has been carried out by differential scanning calorimetry (DSC), rheometry and electroconductimetry. DSC performed on steadily cooled emulsions has shown the presence of a water flux from the inner undercooled phase towards the outer frozen phase; it has been possible to reduce this flux by decreasing the amount of lipophilic surfactant Hypermer A60 in the membrane. Rheometry, electroconductimetry and DSC measurements performed on multiple emulsions diluted at ambient temperature in suitable aqueous glucose solutions have shown the existence of a water flux, the intensity and direction of which were dependent on the osmotic pressure gradient, Delta pi = pi(outer) - pi(inner) existing between the two aqueous phases. When Delta pi was negative (dilution in distilled water), the resultant swelling of the oil globules induced them to burst with the release of the entrapped MgSO4; no release of this compound by diffusion was observed. As for the water transfer at subambient temperature, it was found that the smaller the amount of lipophilic surfactant, the smaller the water flux occurring at ambient temperature. Furthermore, this surfactant also appeared to improve the mechanical resistance of the membrane, and an optimal concentration for the release of the electrolyte was found.