Flocculation and coalescence in water-in-oil emulsions stabilized by paraffin wax crystals

Water-in-mineral oil emulsions were prepared with small amounts of paraffin wax (0-2% w/w) added to the continuous phase, either by addition of pre-crystallized wax to the emulsion prior to emulsification or via subsequent quench-cooling of wax crystals in situ. Stability of the emulsions was examined using pulsed NMR droplet-size analysis, sedimentation and microscopy. Both pre and post-crystallized wax decreased the degree of droplet coalescence, however, emulsions made with post-crystallized wax were more stable over a 10-day period. Microscopy showed that visible crystals were strictly associated with droplets and droplet clusters indicating an affinity of the crystals to the interface. The incorporation of as little as 0.125% wax resulted in a notable decrease in emulsion sedimentation. After 24 days of storage, samples prepared with post-crystallized wax showed no sedimentation or flocculation, unlike pre-crystallized samples which were still somewhat destabilized despite the presence of as much as 2% wax. From these findings, rapid crystallization of wax in the continuous phase of a water-in-oil emulsion following emulsification is an effective means of enhancing long-term stability. (C) 2003 Elsevier Science Ltd. All rights reserved.