Emulsification by Surfactants

Emulsification—the formation of emulsions from two immiscible liquid phases—is probably the most versatile property of surface-active agents for practical applications and, as a result, has been extensively studied. Paints, polishes, pesticides, metal cutting oils, margarine, ice cream, cosmetics, metal cleaners, and textile processing oils are all emulsions or are used in emulsified form. Since there are a number of books and chapters of books devoted to emulsions and emulsification (Sjoblom, 1996 Solans and Kunieda, 1996 Becher, 2001), the discussion here covers only those aspects of emulsification that bear on the role of surfactants in this phenomenon. 

An emulsion is a significantly stable suspension of particles of liquid of a certain size within a second, immiscible liquid. The term significantly stable means relative to the intended use and may range from a few minutes to a few years. Investigators in this field distinguish between three different types of emulsions, based upon the size of the dispersed particles (1) macroemulsions, the most well-known type, opaque emulsions with particles 400 nm (0.4 pm), easily visible under a microscope (2) microemulsions, transparent dispersions with particles 100 nm (0.1 pm) in size and (3) nanoemulsions (miniemulsions), a type that is blue-white, with particle sizes between those of the first two types (100-400 nm [0.1-0.4 pm]. Multiple emulsions (Matsumoto, 1976), in which the dispersed particles are themselves emulsions, have been the subject of considerable investigation. 

Surfactants and Interfacial Phenomena, Third Edition. Milton J. Rosen ISBN 0-471-47818-0 2004 John Wiley Sons, Inc. 

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Self-emulsification The polymer molecules are modified chemically by the introduction of basic (e.g., amino) or acidic (e.g., carboxyl) groups in such concentration and location that the polymer undergoes self-emulsification without surfactant after dispersion in an acidic or basic solution. 

In order to obtain emulsification, a premix of the fluid phases containing surface-active agents and further additives is subjected to high energy for homogenization. Independent of the technique used, the emulsification includes first deformation and disruption of droplets, which increase the specific surface area of the emulsion, and second, the stabilization of this newly formed interface by surfactants. 

Efficient and stable at high temperatures - resistant to emulsification by processing surfactants. 

Crosslinking of the surfactant molecules may be induced by simultaneous activation of two neighbouring molecules with the net result that the molecular weight of the polymer increases until a three dimensional gel network is formed. As the hydrophilic poloxamers are surface-active, promoting o/w emulsification, oil-in-water emulsions may be prepared which contain the poloxamer in the continuous aqueous phase. After emulsification, the surfactant molecules can be crosslinked at the oil-in-water interface and in the continuous phase by Y i.rradiation, forming a network of surfactant molecules which link the dispersed oil globules. 

Other effects of significance for the application of surfactants include forced and spontaneous emulsification, stabilisation of emulsions and dispersions, the wetting of hydrophobic surfaces by surfactants solutions, and many more. 

Pumping with PCPs can be improved by downhole emulsification (25, 115, 116). Downhole emulsification uses surfactants to create oil-in-water emulsions of low viscosity. The benefits of downhole emulsi-... 

The adsorption kinetics of a surfactant to a freshly formed surface as well as the viscoelastic behaviour of surface layers have strong impact on foam formation, emulsification, detergency, painting, and other practical applications. The key factor that controls the adsorption kinetics is the diffusion transport of surfactant molecules from the bulk to the surface [184] whereas relaxation or repulsive interactions contribute particularly in the case of adsorption of proteins, ionic surfactants and surfactant mixtures [185-188], At liquid/liquid interface the adsorption kinetics is affected by surfactant transfer across the interface if the surfactant, such as dodecyl dimethyl phosphine oxide [189], is comparably soluble in both liquids. In addition, two-dimensional aggregation in an adsorption layer can happen when the molecular interaction between the adsorbed molecules is sufficiently large. This particular behaviour is intrinsic for synergistic mixtures, such as SDS and dodecanol (cf the theoretical treatment of this system in Chapters 2 and 3). The huge variety of models developed to describe the adsorption kinetics of surfactants and their mixtures, of relaxation processes induced by various types of perturbations, and a number of representative experimental examples is the subject of Chapter 4. 

Sjo.strom, B., Kronberg, B. and Carlfors, J., A method for the preparation of submicron particles of sparingly water-soluble drugs by precipitation in oil-in-water emulsions. I. Influence of emulsification and surfactant concentration, J. Pharm. Sci, 82, 579-583 (1993). 

To reduce the energy requirement for emulsification, surfactants are usually added to lower the interfacial free energy or interfacial tension. A small quantity of surfactant addition can lower the amount of mechanical energy needed for emulsification by several orders of magnitude (an illustration is provided in [23]). Surfactants adsorb at interfaces, frequently concentrating in one molecular layer at the interface. These interfacial films often provide the stabilizing influence in emulsions since they can both lower interfacial tension and increase the interfacial viscosity. The... 

Shinoda, K. and Saito, H., The stability of O/W type emulsions as fimctions of temperature and the HLB of emulsifiers the emulsification by PIT-method, J. Coll. Interf. ScL 30, 258 263, 1969. Austad, T. and Milter, J., Surfactant flooding in enhanced oil recovery, in Surfactants, Fundamentals and Applications in the Petroleum Industry, Schramm, L.L., Ed., Cambridge University Press, Cambridge, 2000, pp. 203 249. 

The possibility of emulsification. Instead of an inflated micelle (with a size less than 10 nm), what forms here is a larger drop of grease surrounded by surfactant, with an overall size of about 1 Xm). 

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