EFFECT OF COLLOIDAL INTERACTIONS ON THE RATE OF INTERDROPLET HETEROGENEOUS NUCLEATION IN OIL-IN-WATER EMULSIONS

Pulsed nuclear magnetic resonance was used to monitor the crystallizat ion of supercooled liquid droplets in 30 wt% n-hexadecane oil-in-water emulsions at 6 degrees C. Crystallization was induced in the liquid d roplets when solid droplets of the same material were present. The rat e of induced crystallization increased as the concentration of free no n-ionic surfactant (polyoxyethylene sorbitan monolaurate) in the aqueo us phase increased from 0 to 14 wt%. Differential scanning calorimetry measurements indicated that free surfactant had no effect on crystal nucleation of individual droplets. These results indicate that the sur factant enhances induced crystallization by altering colloidal interac tions between droplets. Creaming measurements showed that flocculation was enhanced in emulsions when the free surfactant concentration was increased. We propose that the presence of free surfactant micelles in creases the attraction between droplets because of an osmotic effect, and this attraction facilitates the ability of solid crystals from one droplet to induce crystallization in an adjacent liquid droplet. (C) 1997 Academic Press