Chapter 2
retard water-in-oil emulsion coalescence. They also entrap oil drops and form
aggregates, which results in a rag layer in the middle of the sample. Figure 2.10
shows a partially separated emulsion sample (details can be found in section 4.1)
ofwater in diluted bitumen with a rag layer in the middle. Photomicrographs show
the structure of rag layer. The upper part of the rag layer is water in oil emulsion.
The lower part of the rag layer contains aggregates (skins) of partially oil-wet clay
solid with adsorbed oil and entrapped oil droplets in continuous water phase.
If clay solid becomes more water-wet, it will prefer to stay in water phase
instead of water∕oil interface. Adsorbed oil will be displaced by water and
separated clay solids enter water phase. Thereby the loss of more water wet
solids from the interface will destabilize the emulsion.
Figure 2.10 Rag layer in diluted bitumen emulsion sample
2.7. Reference
[1] J. Sjoblom, Emulsions and emulsion stability, Surfactant science series, CRC
Press, 2006.
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