Emulsions and Microemulsions

The conditions required to form an emulsion of oil and water and a microemulsion. The complex range of structures formed by a microemulsion fluid. Emulsion polymerization and the production of latex paints. Photographic emulsions. Emulsions in food science. Laboratory project on determining the phase behaviour of a microemulsion fluid. 

A simple emulsion can be prepared by shaking a solution of household liquid detergent (washing-up liquid) diluted 1 10 with an equal volume of white spirit (turpentine substitute) or a few drops of cooking oil. The resulting emulsion is stable for several hours. 

Microemulsions can be produced in several ways. One. simple recipe is to use 7 cm3 of household liquid detergent (neat or diluted 1 2), 14 cm3 of white spirit, and 4 cm3 of n-pentanol (amyl alcohol) or n-butanol. The components are mixed gently and allowed to separate into two phases. After several hours the upper oil phase becomes clear but (see Appendix II) exhibits a strong Tyndall cone. This indicates the presence of microemulsion droplets of colloidal size. 

The preparation of polymer latices is a more lengthy process and requires more specialised apparatus and laboratory facilities. A student experiment for the preparation of polystyrene latex by emulsion polymerisation (sec Chapter 4) is described by M. W. J. Eskcr and J. H. A. Picper in Physical Chemistry Enriching Topics from Colloid and Surface Chemistry , cd. H. van Olphen and K. J. Mysels, Theorex, California, 1975. 

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LH Block. Pharmaceutical emulsions and microemulsions. In HA Lieberman, MM Rieger, GS Banker, eds. Pharmaceutical Dosage Forms Disperse Systems, Vol. 2. New York Marcel Dekker, 1996, pp 47-110. 

M.J. Rang and C.A. Miller Emulsions and Microemulsions—Spontaneous Emulsification of Oil Drops Containing Surfactants and Medium-Chain Alcohols. Prog. Colloid Polym. Sci. 109, 101 (1998). 

M.P. Krafft, A. Chittofrati, J.G. Riess, Emulsions and microemulsions with a fluorocarbon phase, Curr. Opin. Colloid Interface Sci. 8 (2003) 251-258. 

The scientists have used numerous techniques, from pH manipulations to complexations with cyclodextrin to emulsions and microemulsions. All of these techniques are well described by my fellow authors in this book. 

In addition to the concepts such as emulsions, submicron emulsions, and microemulsions introduced in Chapter 10 (Part I Parenteral Applications), the following concepts and background information are important for oral formulations. 

Pramod K. Gupta and John B. Cannon. 2000. Emulsion and Microemulsions for Drug Solubilization and Delivery, inV feter-lnsoluble Drug Formulatiqnedited by Rong Liu, First edition, Interpharm/CRC, pp. 169-212. 

Surfactants have been the most investigated chemicals to promote drug absorption from all body tracts. In this section, we will focus on work carried out from the early stages on the enhancing effects of surfactants on drug GI absorption as well as on their interactions with the GI membrane and their toxicity. Systems with multifactorial effects such as emulsions and microemulsions are not the focus of this review. 

The interfacial tension is a key property for describing the formation of emulsions and microemulsions (Aveyard et al., 1990), including those in supercritical fluids (da Rocha et al., 1999), as shown in Figure 8.3, where the v-axis represents a variety of formulation variables. A minimum in y is observed at the phase inversion point where the system is balanced with respect to the partitioning of the surfactant between the phases. Here, a middle-phase emulsion is present in equilibrium with excess C02-rich (top) and aqueous-rich (bottom) phases. Upon changing any of the formulation variables away from this point—for example, the hydrophilie/C02-philic balance (HCB) in the surfactant structure—the surfactant will migrate toward one of the phases. This phase usually becomes the external phase, according to the Bancroft rule. For example, a surfactant with a low HCB, such as PFPE COO NH4+ (2500 g/mol), favors the upper C02 phase and forms w/c microemulsions with an excess water phase. Likewise, a shift in formulation variable to the left would drive the surfactant toward water to form a c/w emulsion. Studies of y versus HCB for block copolymers of propylene oxide, and ethylene oxide, and polydimethylsiloxane (PDMS) and ethylene oxide, have been used to understand microemulsion and emulsion formation, curvature, and stability (da Rocha et al., 1999). 

Understanding surfactant phase behavior is important because it controls physical properties such as rheology and freeze-thaw stability of formulations. It is also closely related to the ability to form and stabilize emulsions and microemulsions. Micelles, vesicles, mi-croemulsions and liquid crystal phases have all been used as delivery vehicles for perfumes or other active ingredients. 

A second group of researchers has noted a parallelism between emulsions and microemulsions formed with surfactants possessing a poly(ethylene oxide) head group [6,7], The emulsions were of the oil in water (O/W) kind at low tempera-... 

Li Y, Friberg S. Course Manual for the American Chemical Society Short Course on Surfactant Micelles, Liposomes, and Liquid Crystals in Emulsions and Microemulsions. 2002. 

Crude oil becomes trapped in porous media as a result of capillary forces. The reduction of these forces is required for the recovery of residual oil, and this is the basis of enhanced oil recovery. In practice capillary forces are reduced primarily by lowering interfacial tension between oil and water phases, although increasing the viscosity of the water is also important. Lowering interfacial tension leads to the formation of emulsions and microemulsions, which are of great importance in enhanced oil recovery techniques. 

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