Multiple emulsions defined

Emulsions are defined as disperse multi-phase systems of immiscible liquids. In simplest terms, they are either oil-in-water (O/W) or water-in-oil (W/O), where the dispersed phase is listed first and exists as discrete droplets within the continuous phase. In some cases, multiple emulsions can be formed, such as water-in-oil-in-water (W/O/W). Both natural and manufactured emulsions have been studied and utilized extensively, especially within the past 200 years, and Lissant has given an historical overview of the subject [106]. 

Emulsions can be defined as a mixture of at least two inmiscible liquid or liquid crystal phases with the interface being stabilized by an adsorbed monomo-lecular or micellar layer of surface active agents as shown in Fig. 1. Depending on the nature of the dispersed and the continuous phase, different types of emulsions can be distinguished oil-in-water (0/W) or water-in-oil (W/0) emulsions. If the dispersed phase represents an emulsion itself the systems formed are called multiple emulsions. 

Emulsions are defined as dispersions of one liquid in another, stabilized by an interfacial film of emulsifiers such as surfactants and lipids. Emulsion formulations include water in od and oil in water emulsions, multiple emulsions, microemulsions, microdroplets, and liposomes. Microdroplets are unilamellar phospholipid vesicles that consist of a spherical lipid layer with an oil phase inside. 

Figure 5.20 WPI/xanthan gum ratio (wt/wt) influence on the phase angle 5 (degrees) of multiple emulsion droplets, immediately after preparation. The phase angle 5 was defined as arctan(G7G ), where G is the storage modulus, G" is the loss modulus, and tan(5) = G"/G (Benichou et al., 2002b).

Theory The release under shear of an active molecule that is initially encapsulated in the aqueous phase of a W/OAV multiple emulsion is a very promising phenomenon for applications in cosmetics or pharmaceuticals. Taylor (Taylor, 1932, 1934) was first to study the deformation of molecules under shear and their bursting in a simple, dilute emulsion. He considered that breakup occurred when shear stress exceeds cohesion stress. He defined this breakup by way of a capillary number, Ca ... 

An emulsion liquid membrane (ELM) system has been studied for the selective separation of metals. This system is a multiple phase emulsion, water-in-oil-in-water (W/O/W) emulsion. In this system, the metal ions in the external water are moved into the internal water phase, as shown in Fig. 3.4. The property of the ELM system is useful to prepare size-controlled aiKl morphology controlled fine particles such as metals, carbonates/ and oxalates.Rare earth oxalate particles have been prepared using this system, consisting of Span83 (sorbitan sesquioleate) as a surfactant and EHPNA (2-ethyl-hexylphospholic acid mono-2-ethylhexyl ester) as an extractant. In the case of cerium, well-defined and spherical oxalate particles, 20 - 60 nm in size, are obtained. The control of the particle size is feasible by the control of the feed rare earth metal concentration and the size of the internal droplets. Formation of ceria particles are attained by calcination of the oxalate particles at 1073 K, though it brings about some construction of the particles probably caused by carbon dioxide elimination. 

An emulsion is defined as a dispersion of two immiscible liquids, one of which is finely subdivided and uniformly distributed as droplets (the dispersed phase) throughout the other (the continuous phase). A third component (or multiple additional components), the emulsifying agent(s), is necessary to help stabilize the emulsion. The emulsifying agent(s) coats the droplets and prevents droplet coalescence by either reducing the interfacial tension or by creating a physical repulsion between the droplets. The dispersed phase is occasionally also defined as the internal phase the continuous phase is occasionally also defined as the external phase or dispersion medium. Virtually all emulsions are inherently physically unstable. 

For a molecule with a high aqueous solubility, the use of a water-in-oil two-phase emulsion or a multiple phase water-in-oil-in-water emulsion may enable a measure of sustained-release to be achieved. In either case, the nature of the sustained-release delivery profile will be a function of the partition coefficient of the molecule between the two phases, which will define the rate at which the molecule is available for absorption. 

Oral solutions, emulsions and suspensions are defined as being supplied in single-dose or multidose containers. Each dose from a multidose container is administered by means of a device suitable for measuring the prescribed volume. The device is usually a spoon or a cup for volumes of 5 mL or multiples thereof or an oral syringe for other volumes. 

For bridging flocculation to occur, several conditions must be met. The most obvious is that the droplet surfaces must be subject to polymer adsorption. In emulsions, the presence of surfactants at the interface, which are necessary for coalescence stability, means that only polymers with sufficient surface affinity to displace the surfactant from the siuface, or a specific affinity for the surfactant itself, may adsorb. A second condition places a lower limit on the size of the polymers in a given system. Clearly the partially coated droplets must encounter one another, coming close enough for a polymer molecule to span the gsq> between the droplets. This means that the polymer molecules must be able to extend past the primary maximum in the total interaction potential. The absolute limit on polymer size will be defined by the position of the primary maximum and the radius of gyration of the polymer molecules. However, in practice, when polymer molecules become adsorbed to drop surfaces the conformation of the polymer molecule frequently alters to allow multiple attachments to the drop surface, which may reduce the distance the polymer extends into solution. 

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