Coarse emulsion

Thin beds will separate coarse emulsions (50-/ droplets), but a bed of several inches is required to coalesce secondary emulsions of submicron drops (BIO). Beds of less than one inch have been successfully used to remove water from petroleum fractions. 

Although Stokes law does not apply to particles so small that the Brownian movement influences the rate of gravitational settling, yet for the relatively coarse emulsions prepared in this way, no sensible error is introduced. 

Table 7.1 shows that rather similar results were also found by Makri et al. (2005) for samples of coarse emulsions containing thermodynamically incompatible mixtures of legume seed protein + xanthan gum. The protein surface load was found to be enhanced in the presence of xanthan gum, especially at elevated ionic strengths. That is, there was observed to be an increase in the adsorption of legume seed proteins at the surface of the emulsion droplets which could be attributed to an increase in the thermodynamic activity of the proteins in the system in the presence of the incompatible polysaccharide (see Table 7.1). Associated with the greater extent of protein adsorption, the authors reported an enhancement in the emulsion stability.

The average particle size is at the upper end of the colloidal size range (on the order of micrometers), and the particles are usually visible in a light microscope. We shall describe these as coarse emulsions when we want to emphasize their size range. Because the particles are relatively large and polydisperse, coarse emulsions look white when examined visually. 

Microemulsions contain particles at least an order of magnitude smaller than those in coarse emulsions. 

Microemulsions form spontaneously coarse emulsions ordinarily require vigorous stirring. 

Microemulsions are stable with respect to separation into their components coarse emulsions may have a degree of kinetic stability, but ultimately separate. 

Emulsion polymerization is applicable only to monomers that are relatively insoluble in water, such as styrene. A coarse emulsion of monomer in aqueous surfactant is prepared with a water-soluble initiator, say, H202 in the solution. The surfactant concentration is above the CMC, so surfactant molecules are present as monomers, micelles, and emulsifiers at the oil-water interface. Even an insoluble liquid like styrene dissolves in water to some extent. Therefore the monomer is present in coarse emulsion drops, solubilized in micelles, and as dissolved molecules in water. A schematic illustration of the distribution of surfactant, monomer, and polymer in an emulsion polymerization process is shown in Figure 8.14. 

What are micro emulsions1. How do they differ from coarse emulsions ... 

Many of these variables have been outlined and discussed by Reineccius et al G), One problem that is of concern when encapsulating citrus oils is the extent to which the flavor is incorporated into the carrier solution before drying. The solution can be mixed just enough to disperse the flavor, creating a coarse emulsion or it can be homogenized to create a fine... 

Newton, MA). Microfluidization based on patented technology in which a split feed stream flows into an interaction chamber at ultrahigh velocities and pressures (up to 1500 ft and 16,000 psi respectively). The two streams collide head-on and exit the chamber at a right angle to the collision. The force of the collision creates cavitation and shear forces to decrease the particle size. The feed stream was prepared in a manner similar to the coarse emulsion in which the orange oil was blended into the carrier solution with a whisk. The Microfluidizer was operated at a pressure of 11,000 psi and the sample was collected after one pass through the interaction chamber. 

The extractable surface oil results of the spray dried powders are listed in Table IV. The extractable surface oil decreased as the emulsion size decreased. Based on previous knowledge, one would anticipate that less surface oil would result in a better shelf-life. The results of this study do not support that theory especially when you consider the third set of samples in which the coarse emulsion had the greatest amount of extractable surface oil yet also had the longest shelf-life. 

It was observed that the titration of a coarse emulsion by a coemulsifier (a macromonomer) leads in some cases to the formation of a transparent microemulsion. Transition from opaque emulsion to transparent solution is spontaneous and well defined. Zero or very low interfacial tension obtained during the redistribution of coemeulsifier plays a major role in the spontaneous formation of microemulsions. Microemulsion formation involves first a large increase in the interface (e.g., a droplet of radius 120 nm will disperse ca. 1800 microdroplets of radius 10 nm - a 12-fold increase in the interfacial area), and second the formation of a mixed emulsifier /coemulsifier film at the oil/water interface, which is responsible for a very low interfacial tension. 

The most significant difference between emulsions (opaque) and microemulsions (transparent) lies in the fact that stirring or increasing the emulsifier concentration usually improves the stability of coarse emulsion. This is not the case with microemulsions - their formation depends on specific interactions among the constituent molecules. If these interactions are not realized, neither intensive stirring nor increasing the emulsifier concentration will produce a microemulsion. On the other hand, once the conditions are right, spontaneous formation occurs and little mechanical work is required [26]. 

Microemulsions, like micelles, are considered to be lyophilic, stable, colloidal dispersions. In some systems the addition of a fourth component, a co-surfactant, to an oil/water/surfactant system can cause the interfacial tension to drop to near-zero values, easily on the order of 10-3 - 10-4 mN/m, allowing spontaneous or nearly spontaneous emulsification to very small drop sizes, typically about 10-100 nm, or smaller [223]. The droplets can be so small that they scatter little light, so the emulsions appear to be transparent. Unlike coarse emulsions, microemulsions are thought to be thermodynamically stable they do not break on standing or centrifuging. The thermodynamic stability is frequently attributed to a combination of ultra-low interfacial tensions, interfacial turbulence, and possibly transient negative interfacial tensions, but this remains an area of continued research [224,225],... 

Both crossflow and deadend systems can be used in premix and direct membrane emulsification. In the crossflow premix system the coarse emulsion is diluted by permeation into pure continuous phase/diluted emulsion recirculating at the low-pressure side of the membrane. In the deadend system the fine emulsion is withdrawn as a product after passing through the membrane, without any recirculation and/or dilution with the continuous phase. In this process, the fine emulsion can... 

The term ME is often incorrectly used in the literature to describe oil and water dispersions of small droplet size produced by prolonged ultrasound mixing, high-shear homogenization, and microfluidisation, that is, submicrometer emulsions. The major differences between a microemulsion and a coarse emulsion are shown in Table 1. 

Add the oil phase to the water phase and continue the heating up to 80°C with constant stirring to form a coarse emulsion. 

Emulsification In the 1990s, Suzuki found a new method to produce emulsions, once more using membranes (Suzuki et al. 1996 Suzuki et al. 1998). In this case, he did not have a to-be-dispersed phase at one side and a continuous phase at the other side, but he started with a coarse pre-emulsion, featuring large droplets. He then simply pushed this coarse emulsion through a porous membrane. At the other side, he observed a fine emulsion emerging that had a narrow droplet size distribution (see Figure 15.19). 

Flgiire 15.19. The Suzuki flow-through membrane emulsification. A coarse emulsion is pressed... 

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