Two effects of wax crystals on stabilizing water-in-oil emulsions

Research shows that the wax crystals precipitated in crude oil emulsions can not only form a three-dimensional network, but also be adsorbed at the oil-water interface, which prevents the coalescence of water droplets and thus enhances the stability of the water-in-oil (W/O) emulsions. A deeper exploration on the crystallization behavior of wax crystals at the interface and the specific roles of wax crystals and droplets played during the network formation process in the W/O model oil emulsions was conducted in this study through interfacial experiments, microscopic observation and rheological measurement. The results show that the emulsifier can promote the crystallization of paraffin wax at the interface if the wax molecules are able to co-crystallize with the emulsifier. It helps to form an elastic interfacial film, preventing the water droplet coalescence. The droplets covered with wax crystals can participate in the network forming process and play a leading role. It is further discovered that the crystals formed by the binding of the wax molecules and the emulsifier molecules become spherical and not prone to overlap with each other. By contrast, no crystallization of paraffin wax will take place on the surface of droplets when there is no co-crystallization effect between the paraffin wax and the emulsifier. Under this circumstance, the wax crystals are slender and needle-like, and are easily overlapped with each other. As a result, the wax crystals play a dominant role in the network forming process.