Behavior of Drops in an Emulsion

The behavior of emulsions is considered in Section V in connection with the process of oil dehydration. Actual problems of drop integration in emulsions are discussed. It is shown that this process occurs most effectively if the emulsion is subjected to an electric field. In this context, the behavior of conducting drops in emulsions, the interaction of drops in an electric field, and the coalescence of drops in emulsions are examined in detail. In terms of applications, processes of emulsion separation in settling tanks, electro dehydrators, and electric filters are considered. 

The behavior of disperse systems, such as foams and emulsions, is very complex and there have been only few attempts to derive qualitative and quantitative relationships between their stability and physicochem-ical parameters of the stabilizing adsorption layers. The starting point of most of these approaches is the hydrodynamic theory of thinning of a liquid film between two bubbles or drops according to Reynolds (1) and Levich (2). A simplified picture of the general scenario in an emulsion is the following. When two... 

Hayashi et al., 1989], involving the addition of monomer and initiator to a previously prepared emulsion of polymer particles, is especially useful for this purpose since it allows the variation of certain reaction parameters while holding N constant. Thus, h in seeded styrene polymerization drops from 0.5 to 0.2 when the initiator concentration decreases from 10-2 to 1CT5 M. At sufficiently low Ru the rate of radical absorption is not sufficiently high to counterbalance the rate of desorption. One also observes that above a particular initiation rate ([I] = lO-2 M in this case), the system maintains case 2 behavior with h constant at 0.5 and Rp independent of Ri. A change in Ri simply results in an increased rate of alternation of activity and inactivity in each polymer particle. Similar experiments show that h drops below 0.5 for styrene when the particle size becomes sufficiently small. The extent of radical desorption increases with decreasing particle size since the travel distance for radical diffusion from a particle decreases. 

The transition from the three-phase to two-phase region in the PDM system was marked by a sudden increase of spontaneous emulsification in the oil phase. Because formation of an intermediate microemulsion ceased at this point, the emulsion drops remained near the brine interface rather than rapidly moving away to form a single-phase region above the brine. An example of this behavior is shown in Figure 15 for the 2.1 gm/dl-salinity PDM system. 

The behavior of thin liquid films formed between coalescing drops and bubbles has attracted considerable attention in an attempt to understand the stabilizing mechanisms of emulsions and foams. It is now generally recognized that the drainage of this film plays a crucial role in determining the stability of the dispersion. 

In concentrated emulsions the fluidity index n is less than unity, which is an indication of shear thinning or pseudoplastic behavior. Figure 6 indicates flie shear stress-shear rate rheogram for 0/W emulsions with different oil contents and similar drop size. The straight line variation is indicative of the compliance with the power-law model. The slope, i.e., the fluidity index n in this plot, is essentially unity up to 50% internal phase, then it tends to decrease as the internal phase content increases (black lines with no data points in Fig. 6). 

---