Phases water-in-oil

Eccleston GM. Multiple-phase oil-in-water emulsions. J Soc Cosmet Chem 1990 41 1-22. 

Lif and Holmberg have demonstrated the efficiency of microemulsions as a medium for both organic and bioorganic hydrolysis of a 4-nitrophenyl ester see Scheme 3 of Fig. 3 [7]. The reactions were performed in a Winsor I type microemulsion and took place in the lower phase oil-in-water microemulsion. After the reaction was complete a Winsor I—>111 transition was induced by a rise in temperature. The products formed, 4-nitrophenol and decanoic acid, partitioned into the upper oil phase and could easily be isolated by separation of this phase and evaporation of the solvent. The principle is outlined in Fig. 4. The surfactant and the enzyme (in the case of the lipase-catalysed reaction) resided in the middle-phase microemulsion and could be reused. 

After describing the experimental technique in the next section, we report our observations of intermediate phase formation and spontaneous emulsification in three parts corresponding to three types of equilibrium phase behavior found when equal volumes of oil and the surfactant-alcohol-brine mixtures are equilibrated. The three types are well known (8-9) and, in order of increasing salinity, are a "lower" phase, oil-in-water microemulsion in equilibrium with excess oil, a "surfactant" or "middle" phase, probably of varying structure, in equilibrium with both excess oil and excess brine, and an "upper" phase, water-inoil microemulsion in equilibrium with excess brine. 

Many successful formulations are based on emulsion techniques. In these formulations, oil and water are mixed in such a way that small, uniformly shaped oil droplets are dispersed in the water phase (oil in water) or water droplets are dispersed in a continuous oil phase (water in oil). An emulsion appears as a cloudy suspension. When an oil-in-water emulsion has oil droplets so small as to produce a clear solution, then formulation is called a microemulsion. The oil phase of the emulsion can provide lipophilic proteins with some protection from enzymatic digestion while the product is in the intestinal tract. Water-in-oil microemulsion formulations have been developed for oral insulin delivery.50... 

An emulsion is an intimate mixture of oil and water, generally of a milky or cloudy appearance. Emulsions may be of two types oil-in-water (where water is the continuous phase) and water-in-oil (where water is the discontinuous phase). Oil-in-water emulsions are used as cutting fluids because of the need for the cooling effect of the water. Water-in-oil emulsions are used where the oil, not the water, must contact a surface-as in rust preventives, non-flammable hydraulic fluids, and compounded steam cylinder oils such emulsions are sometimes referred to as inverse emulsions. Emulsions are produced by adding an emulsifier. Emulsibility is not a desirable characteristic in certain lubricating oils, such as crankcase or turbine oils, that must separate from water readily. Unwanted emulsification can occur as a result of oxidation products--which are usually polar compounds—or other contaminants in the oil. 

An emulsion is a disperse system of at least two immiscible liquids, e.g. water and oil. One of these phases is finely dispersed and forms droplets in the other phase. Depending on the droplet phase, oil-in-water (o/w) and water-in-oil- (w/o) types of emulsion exist. Droplet sizes usually range from 0.1 to 1 pm in mini- or submicron emulsions and from 1 to several tens of pm in (macro-) emulsions. 

Consideration of Equation 7.33 shows immediately that the vehicle has an influence on the absorption of the drug if the vehicle is changed so that the drug becomes less soluble in it, P increases so that permeability increases. The vehicle is more dominant in topical therapy than in most routes of administration because the vehicle remains at the site, although not always in an unchanged form. Evaporation of water from the base would leave drug molecules immersed in the oily phase. Oil-in-water emulsion systems may invert to water-in-oil systems. 

Lif and Holmberg [3] have demonstrated the efficiency of microemulsions as a medium for both organic and bioorganic hydrolyses of a 4-nitrophenyl ester see Fig. 1. The reactions were performed in a Winsor I type of microemulsion and took place in the lower phase oil-in-water microemulsion. 

Although it is hard to draw a sharp distinction, emulsions and foams are somewhat different from systems normally referred to as colloidal. Thus, whereas ordinary cream is an oil-in-water emulsion, the very fine aqueous suspension of oil droplets that results from the condensation of oily steam is essentially colloidal and is called an oil hydrosol. In this case the oil occupies only a small fraction of the volume of the system, and the particles of oil are small enough that their natural sedimentation rate is so slow that even small thermal convection currents suffice to keep them suspended for a cream, on the other hand, as also is the case for foams, the inner phase constitutes a sizable fraction of the total volume, and the system consists of a network of interfaces that are prevented from collapsing or coalescing by virtue of adsorbed films or electrical repulsions. 

An emulsion may be defined as a mixture of particles of one liquid with some second liquid. The two common types of emulsions are oil-in-water (O/W) and water-in-oil (W/0), where the term oil is used to denote the water-insoluble fiuid. These two types are illustrated in Fig. XIV-1, where it is clear that the majority or outer phase is continuous, whereas the minority or inner phase is not. These two emulsion types are distinguished by their ability to disperse oil or water-soluble dyes, their dilution with oil or water, and their conductivity (O/W emulsions have much higher conductivity than do W/0 ones see Ref. 1 for reviews). 

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). 

When the propellant is in the internal phase (Fig. 2a), the propellant vapor, upon discharge, must pass through the emulsion formulation in order to escape into the atmosphere. In traveling through this emulsion, the trapped propellant forms a foam matrix. These systems, are typically oil-in-water emulsions. 

Solvent Evaporation. This encapsulation technology involves removing a volatile solvent from either an oil-in-water, oil-in-oil, or water-in-oH-in-water emulsion (19,20). In most cases, the shell material is dissolved in a volatile solvent such as methylene chloride or ethyl acetate. The active agent to be encapsulated is either dissolved, dispersed, or emulsified into this solution. Water-soluble core materials like hormonal polypeptides are dissolved in water that contains a thickening agent before dispersion in the volatile solvent phase that contains the shell material. This dispersed aqueous phase is gelled thermally to entrap the polypeptide in the dispersed aqueous phase before solvent evaporation occurs (21). 

Suspensions of oil in water (32), such as lanolin in wool (qv) scouring effluents, are stabilized with emulsifiers to prevent the oil phase from adsorbing onto the membrane. Polymer latices and electrophoretic paint dispersions are stabilized using surface-active agents to reduce particle agglomeration in the gel-polarization layer. 

The most common types of emulsions consist of only two Hquids, water and an oil. An o/w emulsion consists of oil droplets dispersed in a continuous aqueous phase, and a w/o emulsion consists of water droplets dispersed in oil (Fig. 1). Occasionally inversion takes place an o/w emulsion changes into w/o emulsion and vice versa. More complex emulsions such as double emulsions are formed because the water droplets in a continuous oil phase themselves contain dispersed oil droplets (Fig. 2). Such oil-in-water-in-oil emulsions are noted as o/w/o. In the same manner a w/o/w emulsion may be formed, which finds use as a system for slow deHvery, extraction, etc (6,7). 

The pelobischofite-surfactant mixtures emulsifying ability was estimated by measurements of the phase immiscibility time for standard oil in water emulsion. The measurements of emulsion particles size were also carried out. The experiments showed the essential increase of phase immiscibility time with the pelobischofite contents increase. Some decrease in average particles size of standard emulsion was also registered. The emulsifiability of other magnesium containing preparations was at least twice worse. 

The products are available as tablets, capsules, liquids (in the form of solutions, suspensions, emulsions, gels, or injectables), creams (usually oil-in-water emulsions), ointments (usually water-in-oil emulsions), and aerosols, which contain inhalable products or products suitable for external use. Propellants used in aerosols include chlorofluorocarbons (CFCs), which are being phased out. Recently, butane has been used as a propellant in externally applied products. The major manufactured groups include ... 

The most important feature of o/w suspension polymerization is the formation of an oil droplet suspension of the monomer in the water and the maintenance of the individual droplets throughout the polymerization process. Droplet formation in an oil-in-water mixture is accomplished and controlled by two major factors mechanical stirring and the volume ratio of the monomer phase to water. The stirring speed is a key factor in controlling the size of oil droplets and the final size of the polymers. The stirring speed usually needs to be over... 

Emulsions. Emulsions are formed when one liquid is dispersed as small droplets in another liquid with which the dispersed liquid is immiscible. Mutually immiscible fluids, such as water and oil, can be emulsified by stirring. The suspending liquid is called the continuous phase, and the droplets are called the dispersed (or discontinuous) phase. There are two types of emulsions used in drilling fluids oil-in-water emulsions that have water as the continuous phase and oil as the dispersed phase, and water-in-oil emulsions that have oil as the continuous phase and water as the dispersed phase (invert emulsions). 

The multiple emulsion technique includes three steps 1) preparation of a primary oil-in-water emulsion in which the oil dispersed phase is constituted of CH2CI2 and the aqueous continuous phase is a mixture of 2% v/v acetic acid solution methanol (4/1, v/v) containing chitosan (1.6%) and Tween (1.6, w/v) 2) multiple emulsion formation with mineral oil (oily outer phase) containing Span 20 (2%, w/v) 3) evaporation of aqueous solvents under reduced pressure. Details can be found in various publications [208,209]. Chemical cross-linking is an option of this method enzymatic cross-linking can also be performed [210]. Physical cross-linking may take place to a certain extent if chitosan is exposed to high temperature. 

On a microscopic scale, a microemulsion is a heterogeneous system and, depending on the relative amounts of the constituents, three main types of structures can be distinguished [69] oil in water (OAV, direct micellar structure), water in oil (W/O, reverse micellar structure) and a bicontinuous structure (B) (Figure 6.1). By adding oil in water, OAV dispersion evolves smoothly to a W/O dispersion via bicontinuous phases. 

Emulsions, especially oil-in-water emulsions which, incidentally, figure widely in cosmetic products, are especially prone to failure because the preservative may partition into the oily phase of the emulsion while contaminants will flourish in the aqueous phase now deprived of preservative by partitioning (see Chapter 18 for further details). 

In a multiphase formulation, such as an oil-in-water emulsion, preservative molecules will distribute themselves in an unstable equilibrium between the bulk aqueous phase and (i) the oil phase by partition, (ii) the surfactant micelles by solubilization, (iii) polymeric suspending agents and other solutes by competitive displacement of water of solvation, (iv) particulate and container surfaces by adsorption and, (v) any microorganisms present. Generally, the overall preservative efficiency can be related to the small proportion of preservative molecules remaining unbound in the bulk aqueous phase, although as this becomes depleted some slow re-equilibration between the components can be anticipated. The loss of neutral molecules into oil and micellar phases may be favoured over ionized species, although considerable variation in distribution is found between different systems. 

The solubility of antioxidants determines their phase distribution in foods. It has been observed that compared to lipid-soluble antioxidants water-soluble antioxidants like ascorbate yield better protection to strongly lipophilic food systems like pure oils. In contrast, antioxidants soluble in lipids like the tocopherols yield better protection to oil-in-water emulsions when compared to water-soluble antioxidants (Porter, 1993). The explanation offered for this... 

The effect of various types of inhibitors with respect to structure and solubility on the formation of N-Nitrosodiethanolamine was studied in a prototype oil in water anionic emulsion, Nitrosation resulted from the action of nitrite on diethanolamine at pH 5.2-5.A, Among the water soluble inhibitors incorporated into the aqueous phase, sodium bisulfite and ascorbic acid were effective. Potassium sorbate was much less so. The oil soluble inhibitors were incorporated into the oil phase of the emulsion. 

The oil phase included a fatty acid, a fatty alcohol and hydrocarbons. The emulsion had a pH of 5.1 to 5.4, exhibited emulsion and pH stability at 37 for at least 21 days, and was shown to be an oil-in-water type by being readily dispersible in water and by its uptake of a water-soluble dye. In inhibition... 

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