Three-phase emulsion

The traditional view of emulsion stability (1,2) was concerned with systems of two isotropic, Newtonian Hquids of which one is dispersed in the other in the form of spherical droplets. The stabilization of such a system was achieved by adsorbed amphiphiles, which modify interfacial properties and to some extent the colloidal forces across a thin Hquid film, after the hydrodynamic conditions of the latter had been taken into consideration. However, a large number of emulsions, in fact, contain more than two phases. The importance of the third phase was recognized early (3) and the lUPAC definition of an emulsion included a third phase (4). With this relation in mind, this article deals with two-phase emulsions as an introduction. These systems are useful in discussing the details of formation and destabilization, because of their relative simplicity. The subsequent treatment focuses on three-phase emulsions, outlining three special cases. The presence of the third phase is shown in order to monitor the properties of the emulsion in a significant manner. 

The final factor influencing the stabiHty of these three-phase emulsions is probably the most important one. Small changes in emulsifier concentration lead to drastic changes in the amounts of the three phases. As an example, consider the points A to C in Figure 16. At point A, with 2% emulsifier, 49% water, and 49% aqueous phase, 50% oil and 50% aqueous phase are the only phases present. At point B the emulsifier concentration has been increased to 4%. Now the oil phase constitutes 47% of the total and the aqueous phase is reduced to 29% the remaining 24% is a Hquid crystalline phase. The importance of these numbers is best perceived by a calculation of thickness of the protective layer of the emulsifier (point A) and of the Hquid crystal (point B). The added surfactant, which at 2% would add a protective film of only 0.07 p.m to emulsion droplets of 5 p.m if all of it were adsorbed, has now been transformed to 24% of a viscous phase. This phase would form a very viscous film 0.85 p.m thick. The protective coating is more than 10 times thicker than one from the surfactant alone because the thick viscous film contains only 7% emulsifier the rest is 75% water and 18% oil. At point C, the aqueous phase has now disappeared, and the entire emulsion consists of 42.3% oil and 57.5% Hquid crystalline phase. The stabilizing phase is now the principal part of the emulsion. 

An emulsion in which the dispersed droplets themselves contain even more finely dispersed droplets of a separate phase. Thus, there can occur oil-dispersed-in-water-dis-persed-in-oil (O/W/O) and water-dispersed-in-oil-dis-persed-in-water (W/O/W) multiple emulsions. These emulsions are sometimes called three-phase emulsions , triple-phase emulsions , or simply triple emulsions . More complicated multiple emulsions such as O/W/O/Wand W/O/W/O are also possible. 

Three-Phase Emulsion Three-Phase Separator Tight Emulsion... 

When a relatively water-insoluble vinyl monomer, such as styrene, is emulsified in water with the aid of anionic soap and adequate agitation, three phases result (see Fig. 6.17) (1) aqueous phase in which a small amount of both monomer and emulsifier are dissolved (i.e., they exist in molecular dispersed state) (2) emulsified monomer droplets which are supercolloidal in size (> 10,000 A), stability being imparted by the reduction of surface tension and the presence of repulsive forces since a negative charge overcoats each monomer droplet (3) submicroscopic (colloidal) micelles which are saturated with monomer. This three-phase emulsion represents the initial state for emulsion polymerization. 

Stage I Stage I begins (see Fig. 6.17) when a free-radical producing water-soluble initiator is added to the three-phase emulsion described above. The commonly used initiator is potassium persulfate, which decomposes thermally to form water-soluble sulfate radical ions ... 

Since the first edition some reviews (and lots of patents) about the application of membranes and membrane reactors have been filed and published (for example [24]). Mostly, special aspects were in the foreground of investigations (such as the interplay of micelles or microemulsions and membranes, interfacial phenomena, three phase emulsion/solid heterogenization, or the properties of metal-based membranes [25]). 

Because three phases are present, the extent of reaction in each phase must be computed. And because the reaction occurs only in the presence of solids, the distribution of solids in the three phases, emulsion, cloud, and bubble, must be known. These are expressed as fractions of the bubble phase, and eb... 

However, the existence and position of these maxima have been found to depend upon other system characteristics as well, and for now, there is no avail able prediction. It is worth noting that the stability minimum corresponds to emulsions that coalesce extremely rapidly. Indeed, it seems that in three phase emulsions that are displayed near SAD = 0, the only delay is the sedimentation process, and that drops coalesce immediately upon contact. Several explanations have been advanced for that (160—162). 

Kunieda, H., and Friberg, S.E. (1986) Foams from a three-phase emulsion. Colloids Surf., 21,17-26. 

Friberg, S. E. (2006). Weight fractions in three-phase emulsions with an La phase. Colloids Surf. A. 282/283, 369-376. 

Nevertheless, possibilities for confusion abound. Until recently (50), it was thought that all nonmultiple emulsions were either oil-in-water (O/W) or water-in-oil (W/O). However, from the definitions of microemulsions and macroemulsions and from Fig. 16.2, it follows that in many macroemulsions one of the two or three phases is a microemulsion. The phase diagram of Fig. 16.2 makes clear that there are six possible nonmultiple, two-phase morphologies, of which four contain a microemulsion phase. These six two-phase morphologies are oleic-in-aqueous (017AQ, or O/W) and aqueous-in-oleic (AQ/OL, or W/O), but also, oleic-in-microemulsion (OL/Ml), microemulsion-in-oleic (MI/OL), aqueous-in-microemulsion (AQ/MI), and microemulsion-in-aqueous (MI/AQ) (50). [Although they have not yet aU been reported, theoretically there are 12 three-phase emulsion morphologies formed by the top, microemulsion (i.e., middle), and bottom phases (51,52) of three-phase microemulsion systems.]... 

Abu-Reziq, R., Avnir, D., and Blum, J. (2002) A three-phase emulsion/solid-heterogenization method for transport and catalysis. Angew, Chem., Int. rf 41 (21), 4132-4134. 

Lin CY, Wang KH. 2003. The fuel properties of three-phase emulsions as an alternative fuel for diesel engines. Fuel 82 1367-1375. 

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