Stabilization of water-in-oil emulsions with continuous phase crystals

The role of continuous phase paraffin wax crystals on water-in-mineral oil emulsion (phi = 0.2) aggregation, coalescence and sedimentation behavior was studied. Paraffin wax crystal properties were controlled by using two crystallization regimes. In regime 1, pre-crystallized wax was added prior to emulsification. In regime 2 (post-crystallization), molten wax was emulsified and quench-crystallized in situ following emulsification. Based on d(0,0) values, all emulsions containing quench-crystallized wax were more stable than their pre-crystallized equivalents (p < 0.05). Sedimentation analyses indicated that, over a 10-day period, regime 2 emulsions with 0.5% (w/w) or more wax in the continuous phase did not phase separate. Only regime 1 emulsions that contained 2% (w/w) added wax did the same. Brightfield and polarized light microscopy revealed the presence of aggregated wax crystal networks in both post-crystallized and pre-crystallized systems. However, the crystals forming the network were much smaller in the former. Atomic force microscopy and X-ray diffraction indicated that the presence of the emulsifier used to aid in emulsion formation also affected wax morphology and polymorphic behavior. In conclusion, due to the presence of a well-defined network structure, emulsions consisting of wax-crystallized in situ were more stable than emulsions with crystals added prior to emulsification. (c) 2005 Elsevier B.V. All rights reserved.