In situ record of the dynamic process of wax deposition in water-in-oil emulsion: Evolution of two types of deposition structures

In this work, the dynamic formation process of wax depositions for a series of water-in-oil emulsions was explored in situ using the PVM (particle video microscope) apparatus. Two types of wax deposition structures were observed: wax crystal clusters enclosing water droplets and water droplet flocs with surfaces covered by wax crystals, either of which could build up a wax deposition. These two structures were formed by the collision, flocculation, aggregation, and encapsulation of two scattered phases: wax crystals and water droplets. The organization of the deposition gradually converted from wax crystal clusters to water droplet flocs was depicted considering the surfactant concentration (0.05, 0.1, 0.5 wt%) and water content (10, 20, 30, 40 vol%) used in emulsion formulation. Furthermore, the variation of water content in the deposition even employing the emulsion with the same water cut was elucidated, which was closely related to these two deposition structures. This in situ study revealed that the surfactant in the wax deposition process of emulsion not only operated as an emulsifier but also tailored the type of deposition structure by inducing the dispersion of wax crystals from oil phase to oil-water interface. These structures partially or entirely involved water droplets into deposition. The findings provide a thorough description of wax deposition formation in water-in-oil emulsions.