Microemulsions and macroemulsions

However, the formal differences between microemulsions and macroemulsions are well defined. A microemulsion is a single, thermodynamically stable, equihbrium phase a macroemulsion is a dispersion of droplets or particles that contains two or more phases, which are Hquids or Hquid crystals (48). 

Nevertheless, possibiUties for confusion abound. From the definitions of microemulsions and macroemulsions and from Figure 1, it immediately follows that in many macroemulsions one of the two or three phases is a microemulsion. Until recentiy (49), it was thought that all nonmultiple emulsions were either oil-in-water (O/W) or water-in-oil (W/O). However, the phase diagram of Figure 1 makes clear that there are six nonmultiple, two-phase morphologies, of which four contain a microemulsion phase. These six two-phase morphologies are oleic-in-aqueous (OL/AQ, or O/W) and aqueous-in-oleic (AQ/OL, or W/O), but also, oleic-in-microemulsion (OL/MI), microemulsion-in-oleic (MI/OL), aqueous-in-microemulsion (AQ/MI), and microemulsion-in-aqueous (MI/AQ) (49). 

A general analysis for microphase catalysis, where microphase includes micelles, swollen micelles, microemulsions and macroemulsions, can be rigorously constructed by writing the... 

RD.I. Eletcher and D.I. Horsup Droplet Dynamics in Water-in-Oil Microemulsions and Macroemulsions Stabilized by Non-Ionic Surfactants. J. Chem. Soc. Earaday Trans. I 88, 855 (1992). 

Obviously, the Bancroft rule is valid for microemulsions and macroemulsions for different reasons. Thermodynamics is responsible for it in the former and kinetics... 

Microemulsion and macroemulsion need to be distinguished. Macroemulsion is a mixture of two or more immiscible (unblendable) liquids. One liquid... 

One primary difference between microemulsion and macroemulsion may be drop size. The size of macroemulsion drops is generally orders of magnimde larger than the size of microemulsion drops. The difference in size explains their difference in properties and appearance however, their fundamental difference is thermodynamic stability (Bourrel and Schechter, 1988). 

Applications of Microemulsions and Macroemulsions of Water and Carbon Dioxide... 

Fletcher, P.D.I. and Horsup, D.I. (1992) Droplet dynamics in water-in-oil microemulsions and macroemulsions stabilized by non-ionic surfactants - correlation of measured rates with monolayer bending elasticity. /. Chem. Soc. Faraday Trans., 88, 855-864. 

Simple anulsions consist of dispersion of droplets of one liquid phase in another inunisable liqnid phase. Based on the type of the internal phase, two types of simple emulsions exist, namely, wato-in-oil (w/o) and oil-in-water (o/w) emulsions (Figures 58.6a and b). In w/o emulsions, the water disperses in the oil continuum phase, whereas, oil phase remains as dispersed in the water continuum phase in o/w emulsions. Emulsifiers are added to fecilitate the reduction in the surface tension amongst the immiscible phases. The type of the emulsions formed is determined by the type of the anulsifier used. Based on the size of the internal phase, simple emulsions can be divided in microemulsions and macroemulsions. If the emulsions contain more than two phases, then they are regarded as multiple emulsions. 

In this chapter, which is a slight elaboration of a recent publication (1), we will discuss how some of our knowledge of microemulsions ean be used in emulsion studies. We discuss in particular the role of phase behavior diffusion studies of both microemulsions and macroemulsions the implications of the flexible surfaee model for emulsion stability and the Ostwald ripening proeess in a potentially metastable emulsion system. By way of these examples it is demonstrated how microemulsion research has helped to develop our current understanding of macroemulsions. 

Macroemulsion and Microemulsion Flooding If a suitable surfactant is injected into the reservoir, it can form macroemulsions and/or microemulsions with the reservoir oil depending on the composition and reservoir conditions. Several articles have been published on the recovery of oil by microemulsion and macroemulsion flooding processes.Among various factors, the most important factor of surfactant flooding in the form of an emulsion is the lowering of the interfacial tension (IFT) at the oil/water interface. Microemulsions are more effective in oil displacement as compared to macroemulsions because microemulsions can provide low IFT systems. 

Microemulsions in selected compositional areas of water-oil-surfactant systems are thermodynamically stable, and isotropic dispersions of nanosized droplets of one liquid in another immiscible liquid (W/O or O/W) are obtained. The water phase, similarly to the case of macroemulsions, could be water in which an alkoxide is to be added, as well as a sol or an alkoxide solution. The difference between microemulsion and macroemulsion systems consists of the amount of surfactants used (10-40% in the former case and 1-2% in the latter case). 

Why must a chapter on macroemulsions consider the phase behavior and thermodynamics of oil-water-surfactant systems at all Indeed, macroemulsions are nonequilibrium systems, whereas the phase behavior concerns thermodynamically stable equilibrium systems — microemulsions and liquid crystals. The reason for it is that microemulsions and macroemulsions normally co-exist in the same system and their properties are interrelated. The surfactant monolayers covering micelles and macroemulsion droplets are in thermodynamic equilibrium. This equilibrium leads to many peculiar effects. 

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