Emulsifier schematic illustration

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. 

A form of liquid membrane that received a great deal of attention in the 1970s and 1980s was the bubble or emulsion membrane, first developed by Li at Exxon [11-13], Figure 11.14 is a schematic illustration of an emulsion liquid membrane process, which comprises four main operations. First, fresh product solution is emulsified in the liquid organic membrane phase. This water/oil emulsion then enters a large mixer vessel, where it is again emulsified to form a water/oil/water emulsion. Metal ions in the feed solution permeate by coupled... 

Latex IPNs. Latex IPNs are the third type of IPNs and are manufactured according to the general schematic illustrated in Figure 3. Latex IPN synthesis involves the initial synthesis of a crosslinked seed polymer, usually in the form of an aqueous latex. The seed latex is then swollen with a second monomer/crosslinker/initiator system which is then polymerized "in situ" to form an aqueous IPN emulsion. Materials of this type are best suited to coating applications as illustrated by the development of "Silent Paint" by Sperling et al ( ). However, latex IPNs are limited to water emulsifiable monomer/polymer systems, most of which have fairly low service temperatures, less than 150 C. 

Single Emulsions. These emulsions are formed by two immiscible phases (e.g. oil and water), which are separated by a surfactant film. The addition of a surfactant (or emulsifier) is necessary to stabilize the drops. The emulsion containing oil as dispersed phase in the form of fine droplets in aqueous phase is termed as oil-inwater (0/W) emulsion, whereas the emulsion formed by the dispersion of water droplets in the oil phase is termed as water-in-oil (W/0) emulsion. Figure 1 schematically illustrates the 0/W and W/0 type emulsions. Milk is an example of naturally occurring 0/W emulsion in which fat is dispersed in the form of fine droplets in water. 

The first step in all interfacial polymerization processes for encapsulation is to form an emulsion. This is followed by initiation of a polymerization process to form the capsule wall. Most commercial products based on interfacial or in situ polymerization employ water-immiscible liquids. For encapsulation of a water-immiscible oil, an oil-in-water emulsion is first formed. Four processes are schematically illustrated in Figure 5.82. In Figure 5.82(a), reactants in two immiscible phases react at the interface forming the polymer capsule wall. For example, to encapsulate a water-immiscible solvent, multifunctional acid chlorides or isocyanates are dissolved in the solvent and the solution is dispersed in water with the aid of a polymeric emulsifier, e.g., poly(vinyl alcohol). When a polyfunctional water-soluble amine is then added with stirring to the aqueous phase, it diffuses to the solvent-water interfece where it reacts with acid chlorides or isocyanates forming the insoluble polymer capsule wall. Normally some reactants with more than two functional groups are used to minimize a regation due to the formation of sticky walls. 

Figure 14 Schematic illustration of possible organization and stabilization mechanism of BSA and monomeric emulsifiers (Span 80) at the two interfaces of double emulsion.

The multiple emulsion is prepared by a two-stage process, as schematically illustrated in Figure 22. The primary emulsion is prepared by adding the aqueous phase to an oil solution of the polymeric emulsifier 1 with a low HLB number, e.g., Aralcel PI 35, using... 

Methods of nanoemulsion preparation have been described in detail. A schematic illustration of the overall process is depicted in Figure 12.2. Three different approaches can be used to incorporate the drug and/or the various components in the aqueous or oil phase. The most common approach is to dissolve the water-soluble ingredients in the aqueous phase and the oil-soluble ingredients in the oil phase. The second approach, which is used in fat emulsion preparations involves the dissolution of an aqueous-insoluble emulsifier in alcohol and then the dispersion of the alcohol solution in water followed by evaporation and total removal of the alcohol until a fine dispersion of the emulsifier in the aqueous phase is reached. The third approach, which is mainly used for hydrophobic drug... 

For initiation in micelles, the emulsifier concentration must exceed the cmc. The classical concept of the cmc is that it represents that concentration at which micelles form at higher concentrations, more micelles form, and at lower concentrations, no micelles are present. The cmc is usually determined by the inflection point in some physical property measured as a function of emulsifier concentration. Figure 1 shows a schematic illustration of the variation of conductivity k, turbidity t, equivalent conductivity X, surface tension y, and osmotic pressure tt with sodium dodecyl sulfate concentration (18). All five parameters show an inflection point at ca. 8mM, which is the most common value of the cmc, and all five curves are consistent with the concept of micelles forming above ca. 8mM and not forming at lower concentrations. Recent measurements of the partial specific volume of sodium lau-ryl sulfate solutions (19), however, suggest that aggregates of lauryl sulfate ions are present of concentrations well below the cmc. 

Figure 13.2 Schematic illustration of an emulsifier molecule and emulsifiers adsorbed at the interface between the phases.

Surfactants as emulsifiers ensure the stability of emulsions. They behave like polar substances which reduce the interfacial tension between the immiscible liquids. Their mode of action can be schematically illustrated as follows [39] ... 

Most monomers polymerizing by the radical mechanism are almost insoluble in water. Intensive stirring of a mixture of such a monomer with water produces an emulsion which remains stable, however, only in the presence of a surface active compound (tenside), e. g. soap. By the addition of a water-soluble initiator to this emulsion, the monomer polymerizes at a rate several times higher than would be observed by any other radical method with an initiator of equal efficiency. At the same time, a higher polymer with a narrower molecular mass distribution is formed. At the initial stages of the reaction, the monomer is present as three types of particle in tenside-stabilized monomer droplets of diameter 10-3 to 10 4cm (about 1012 such droplets are present in 1 cm3 of emulsion of average concentration) in solubilized micelles about 10 nm in size and concentration 1018 cm 3 and in the growing, emulsifier-stabilized monomer—polymer particles 50-100 nm in size. This situation is illustrated schematically in Fig. 14(a). 

In a typical unit, illustrated schematically in Figure 5.15, waste oil-water feed is introduced into an array of membrane modules (four are shown in the figure). Water and low molecular weight solutes (such as salts and some surfactants) pass through the membrane and are removed as permeate. Emulsified oil and any suspended solids are rejected by the membrane and are removed as concentrate. 

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