Emulsion, emulsification

The mechanism of this mini-emulsion emulsification process was investigated by the conductometric titration of aqueous hexadecyltrimethylammonium bromide-cetyl alcohol mixtures with benzene or styrene combined with transmission electron microscopic examination of the morphology of the mixed emulsifiers and the styrene droplets formed (2,8). Figure 1 shows that the titration curves with and without cetyl alcohol are quite different that for... 

The next chapter by G. T. Vladisavljevic and R. A. Williams is a comprehensive and systematic review of new techniques of preparation of multiple emulsions, emulsions, and microparticles. The authors envisage the ways to form multiple droplets by using membrane emulsification processes and microchan-nel and microcapUlary devices. They also pay special attention to the preparation of solid microparticles via a double emulsion emulsification method using membrane emulsification and microfiuidic devices. 

The cleaning process proceeds by one of three primary mechanisms solubilization, emulsification, and roll-up [229]. In solubilization the oily phase partitions into surfactant micelles that desorb from the solid surface and diffuse into the bulk. As mentioned above, there is a body of theoretical work on solubilization [146, 147] and numerous experimental studies by a variety of spectroscopic techniques [143-145,230]. Emulsification involves the formation and removal of an emulsion at the oil-water interface the removal step may involve hydrodynamic as well as surface chemical forces. Emulsion formation is covered in Chapter XIV. In roll-up the surfactant reduces the contact angle of the liquid soil or the surface free energy of a solid particle aiding its detachment and subsequent removal by hydrodynamic forces. Adam and Stevenson s beautiful photographs illustrate roll-up of lanoline on wood fibers [231]. In order to achieve roll-up, one requires the surface free energies for soil detachment illustrated in Fig. XIII-14 to obey... 

It is quite clear, first of all, that since emulsions present a large interfacial area, any reduction in interfacial tension must reduce the driving force toward coalescence and should promote stability. We have here, then, a simple thermodynamic basis for the role of emulsifying agents. Harkins [17] mentions, as an example, the case of the system paraffin oil-water. With pure liquids, the inter-facial tension was 41 dyn/cm, and this was reduced to 31 dyn/cm on making the aqueous phase 0.00 IM in oleic acid, under which conditions a reasonably stable emulsion could be formed. On neutralization by 0.001 M sodium hydroxide, the interfacial tension fell to 7.2 dyn/cm, and if also made O.OOIM in sodium chloride, it became less than 0.01 dyn/cm. With olive oil in place of the paraffin oil, the final interfacial tension was 0.002 dyn/cm. These last systems emulsified spontaneously—that is, on combining the oil and water phases, no agitation was needed for emulsification to occur. 

Monomer emulsions ate prepared in separate stainless steel emulsification tanks that are usually equipped with a turbine agitator, manometer level gage, cooling cods, a sprayer inert gas, temperature recorder, mpture disk, flame arrester, and various nossles for charging the ingredients. Monomer emulsions are commonly fed continuously to the reactor throughout the polymerisation. 

Emulsives are solutions of toxicant in water-immiscible organic solvents, commonly at 15 ndash 50%, with a few percent of surface-active agent to promote emulsification, wetting, and spreading. The choice of solvent is predicated upon solvency, safety to plants and animals, volatility, flammabiUty, compatibihty, odor, and cost. The most commonly used solvents are kerosene, xylenes and related petroleum fractions, methyl isobutyl ketone, and amyl acetate. Water emulsion sprays from such emulsive concentrates are widely used in plant protection and for household insect control. 

Early efforts to produce synthetic mbber coupled bulk polymerization with subsequent emulsification (9). Problems controlling the heat generated during bulk polymerization led to the first attempts at emulsion polymerization. In emulsion polymerization hydrophobic monomers are added to water, emulsified by a surfactant into small particles, and polymerized using a water-soluble initiator. The result is a coUoidal suspension of fine particles,... 

Inversion ofMon cjueous Polymers. Many polymers such as polyurethanes, polyesters, polypropylene, epoxy resins (qv), and siHcones that cannot be made via emulsion polymerization are converted into latices. Such polymers are dissolved in solvent and inverted via emulsification, foUowed by solvent stripping (80). SoHd polymers are milled with long-chain fatty acids and diluted in weak alkaH solutions until dispersion occurs (81). Such latices usually have lower polymer concentrations after the solvent has been removed. For commercial uses the latex soHds are increased by techniques such as creaming. 

Emulsification involves the joining of two mutually insoluble materials, such as petroleum oil and water. The surfactant, which usually has a hydrophilic or water-soluble end and a hydrophobic or oil-soluble end, holds the oil and water together in much the same manner that a fastener holds two pieces of material. Often, the emulsion which forms is unstable, subsequently breaking up and releasing the oil from the water. Break-up is actually preferred, because the oil then floats to the surface, whereas the surfactant is free to emulsify more oil. 

Defoamers (qv) are available in several forms, composed of many different materials. Historically, paste and soHd defoamers were used extensively. Composed of fatty acids, fatty amides, fatty alcohols, emulsifiers (and mineral oil [8012-95-1] in the high soflds paste emulsions), these defoamers required emulsification (brick) or dilution (paste) before use. Liquid defoamers have become the preferred form, insofar as concern about handling and ovemse have been overcome. 

Emulsions. The fatty acid soaps of alkanolamines ate excellent emulsification agents for use in such products as floor poHshes, cosmetics, and functional fluids such as hydrauhc and metalworking fluids. For example, improved hardwater stabiUty of a hydrauhc fluid emulsion is obtained using AMP in the formulation (12). 

In pharmaceutical uses, the general inertness of lanolin and its derivatives, together with their ease of emulsification (185), have been important criteria. These properties are also important in cosmetics, but with emphasis also on the abiHty to absorb large quantities of water or, after suitable modification, to stabilize o/w emulsions. 

De-emulsification, ie, the breaking of foams or emulsions, is an important process, with the oU iadustry being a common one ia which the process is oftea critical. Chemical and particulate agents that displace the surfactant and permit an unstabilized iaterface to form are used for this purpose. 

Emulsification is essential for the development of all types of skin- and hair-care preparations and a variety of makeup products. Emulsions (qv) are fine dispersions of one Hquid or semisoHd ia a second Hquid (the contiauous phase) with which the first substance is not miscible. Generally, one of the phases is water and the other phase is an oily substance oil-ia-water emulsions are identified as o/w water-ia-oil emulsions as w/o. When oil and water are mixed by shaking or stirring ia the absence of a surface-active agent, the two phases separate rapidly to minimize the iaterfacial energy. Maintenance of the dispersion of small droplets of the internal phase, a requirement for emulsification, is practical only by including at least one surface-active emulsifier ia the oil-and-water blend. 

Proper emulsification is essential to the satisfactory performance of a carrier. A weU-formulated carrier readily disperses when poured into water, and forms a milky emulsion upon agitation or steaming. It should not cause oil separation upon heating or crystallization and sedimentation upon cooling. 

Vmulsifier Type. The manufacturers of NBR use a variety of emulsifiers (most commonly anionic) for the emulsion polymerisation of nitrile mbber. When the latex is coagulated and dried, some of the emulsifier and coagulant remains with the mbber and affects the properties attained with the mbber compound. Water resistance is one property ia particular that is dependent on the type and amount of residual emulsifier. Residual emulsifer also affects the cure properties and mold fouling characteristics of the mbber. 

A (macro)emulsion is formed when two immiscible Hquids, usually water and a hydrophobic organic solvent, an oil, are mechanically agitated (5) so that one Hquid forms droplets in the other one. A microemulsion, on the other hand, forms spontaneously because of the self-association of added amphiphilic molecules. During the emulsification agitation both Hquids form droplets, and with no stabilization, two emulsion layers are formed, one with oil droplets in water (o /w) and one of water in oil (w/o). However, if not stabilized the droplets separate into two phases when the agitation ceases. If an emulsifier (a stabilizing compound) is added to the two immiscible Hquids, one of them becomes continuous and the other one remains in droplet form. 

Much commercial equipment is available for emulsification (Fig. 3) and has been well described (9). The following discusses the relations between energy input and emulsion droplet size. 

In the case of emulsions with three liquids the presence of the third phase results in a reduction of the energy input for the emulsification process, whereas the emulsion with a Hquid crystal as the third phase shows interesting stabilization mechanisms. Finally, the emulsion with added particles illustrates the importance of Hquid—solid wetting for stabiHty. 

Liquid Third Phase. A third Hquid with coUoidal stmcture has been a known component in emulsions since the 1970s (22) for nonionic surfactants of the poly(ethylene glycol) alkylaryl ether type. It allows low energy emulsification (23) using the strong temperature dependence of the coUoidal association stmctures in the water—surfactant—hydrocarbon systems. 

At low temperature, nonionic surfactants are water-soluble but at high temperatures the surfactant s solubUity in water is extremely smaU. At some intermediate temperature, the hydrophile—Hpophile balance (HLB) temperature (24) or the phase inversion temperature (PIT) (22), a third isotropic Hquid phase (25), appears between the oil and the water (Fig. 11). The emulsification is done at this temperature and the emulsifier is selected in the foUowing manner. Equal amounts of the oil and the aqueous phases with aU the components of the formulation pre-added are mixed with 4% of the emulsifiers to be tested in a series of samples. For the case of an o/w emulsion, the samples are left thermostated at 55°C to separate. The emulsifiers giving separation into three layers are then used for emulsification in order to find which one gives the most stable emulsion. 

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