Colloidal dispersions emulsions

This book provides an introduction to the colloid and interface science of three of the most common types of colloidal dispersion emulsions, foams, and suspensions. The initial emphasis covers basic concepts important to the understanding of most kinds of colloidal dispersions, not just emulsions, foams, and suspensions, and is aimed at providing the necessary framework for understanding the applications. The treatment is integrated for each major physical property class the principles of colloid and interface science common to each dispersion type are presented first, followed as needed by separate treatments of features unique to emulsions, foams, or suspensions. The second half of the book provides examples of the applications of colloid science, again in the context of emulsions, foams, and suspensions, and includes attention to practical processes and problems in various industrial settings. 

See solution colloidal dispersion emulsion colloid chemistry. 

Colloidal systems and dispersions are of great importance in oil recovery, waist water treatment, coating, food and beverage industry, pharmaceutical industry, medicine, environmental protection etc. Colloidal systems and dispersions are always multi-component and multiphase systems. In these systems at least one dimension is in a range of colloidal forces action colloidal dispersions/emulsions are examples of three dimensional colloidal systems, while thin liquid films are examples of one dimensional colloidal systems. Mostly colloidal systems are stable because their properties are substantially enhanced by the presence of surfactants and or polymers. The distribution and redistribution of the latter molecules is of the crucial importance for colloidal systems. 

The predictions of different quantitative criteria for stability-instability transitions were investigated [461], having in mind that the oscillatory forces exhibit both maxima, which play the role of barriers to coagulation, and minima that could produce flocculation or coalescence in colloidal dispersions (emulsions, foams, suspensions). The interplay of the oscillatory force with the van der Waals surface force was taken into account. Two different kinetic criteria were considered, which give similar and physically reasonable results about the stability-instability transitions. Diagrams were constructed, which show the values of the micelle volume fraction, for which the oscillatory barriers can prevent the particles from coming into close contact, or for which a strong flocculation in the depletion minimum or a weak flocculation in the first oscillatory minimum could be observed [461]. 

In mass polymerization bulk monomer is converted to polymers. In solution polymerization the reaction is completed in the presence of a solvent. In suspension, dispersed mass, pearl or granular polymerization the monomer, containing dissolved initiator, is polymerized while dispersed in the form of fine droplets in a second non-reactive liquid (usually water). In emulsion polymerization an aqueous emulsion of the monomer in the presence of a water-soluble initiator Is converted to a polymer latex (colloidal dispersion of polymer in water). 

The compounding technique for latex differs from that of dry mbber and is fundamentally simpler. A critical factor of colloidal stabiUty makes necessary that each ingredient is of optimum particle size, pH, and concentration when added as an aqueous dispersion to the latex. Rubber latex is a colloidal aqueous emulsion of an elastomer and natural mbber latex is the milky exudation of certain trees and plants that of greatest commercial importance is the... 

Poly(vinyl chloride) is commercially available in the form of aqueous colloidal dispersions (latices). They are the uncoagulated products of emulsion polymerisation process and are used to coat or impregnate textiles and paper. The individual particles are somewhat less than 1 p,m in diameter. The latex may be coagulated by concentrated acids, polyvalent cations and by dehydration with water-miscible liquids. 

A colloidal dispersion of oil-in-water. In BW systems where oil contamination has occurred, emulsifying agents from the oil can produce an emulsion which further adds to the total foulant load and impedes heat-transfer. Specific organic emulsifiers have both hydrophilic (water loving) and lipophilic (oil loving) groups in the same molecule. 

Emulsions and Emulsion Technology (in three parts), edited by Kenneth J. Lissant Anionic Surfactants (in two parts), edited by Warner M. Linfieid see Volume 56) Anionic Surfactants Chemical Analysis, edited by John Cross Stabilization of Colloidal Dispersions by Polymer Adsorption, Tatsuo Sato and Richard Ruch... 

J. Bibette, 1991, (Depletion interactions and fractionated crystallization for poly-disperse emulsion purification), J. Colloid Interface Sci. 147, 474. 

A surfactant is a surface-active agent that is used to disperse a water-insoluble drug as a colloidal dispersion. Surfactants are used for wetting and to prevent crystal growth in a suspension. Surfactants are used quite extensively in parenteral suspensions for wetting powders and to provide acceptable syringability. They are also used in emulsions and for solubilizing steroids and fat-soluble vitamins. 

Forster, Th., von Rybinski, W. and Wadle, A. (1995) Influence of microemulsion phases on the preparation of fine-disperse emulsions. Advances in Colloid and Interface Science, 58, 119-149. 

Most hand creams are colloidal, and generally have a thick, creamy consistency. The majority of hand creams are formulated as a liquid-in-liquid colloid (an emulsion), in which the dispersion medium is water based, and the dispersed phase is an oil such as palm oil or cocoa butter . These oils are needed to replenish in the skin those natural oils lost through excessive heat and work. 

Colloidal suspensions, emulsions and solid dispersions are produced by means of colloid mills or dispersion mills. Droplets or particles of sizes less than 1 (im may be formed, and solids suspensions consisting of discrete solid particles are obtainable with feed material of approximately 100-mesh or 50 p,m in size. 

Another example of a food emulsion is the ice cream, in which the colloidal dispersion of ice particles is achieved together with tiny entrapped air bubbles in an emulsion consisting of fats, sugar, and thickening agents (polysaccharides). 

Emulsion polymerization refers to a unique process employed for some radical chain polymerizations. It involves the polymerization of monomers in the form of emulsions (i.e., colloidal dispersions). The process bears a superficial resemblance to suspension polymerization (Sec. 3-13c) but is quite different in mechanism and reaction characteristics. Emulsion polymerization differs from suspension polymerization in the type and smaller size of the particles in which polymerization occurs, in the kind of initiator employed, and in the dependence of polymer molecular weight on reaction parameters. 

Preparation of Emulsions. An emulsion is a system in which one liquid is colloidally dispersed in another (see Emulsions). The general method for preparing an oil-in-water emulsion is to combine the oil with a compatible fatty acid, such as an oleic, stearic, or rosin acid, and separately mix a proportionate quantity of an alkali, such as potassium hydroxide, with the water. The alkali solution should then be rapidly stirred to develop as much shear as possible while the oil phase is added. Use of a homogenizer to force the resulting emulsion through a fine orifice under pressure further reduces its oil particle size. Liquid oleic acid is a convenient fatty acid to use in emulsions, as it is readily miscible with most oils. 

Emulsions and foams are two other areas in which dynamic and equilibrium film properties play a considerable role. Emulsions are colloidal dispersions in which two immiscible liquids constitute the dispersed and continuous phases. Water is almost always one of the liquids, and amphipathic molecules are usually present as emulsifying agents, components that impart some degree of durability to the preparation. Although we have focused attention on the air-water surface in this chapter, amphipathic molecules behave similarly at oil-water interfaces as well. By their adsorption, such molecules lower the interfacial tension and increase the interfacial viscosity. Emulsifying agents may also be ionic compounds, in which case they impart a charge to the surface, which in turn establishes an ion atmosphere of counterions in the adjacent aqueous phase. These concepts affect the formation and stability of emulsions in various ways ... 

Preparation of an aqueous elastomeric polymer emulsion of colloidally dispersed small particles with a particle size of 0.15-0.22 p,... 

Prepare a little magnesium oleate by treating a solution of sodium oleate with magnesium sulfate. Carefully wash the precipitate free from soluble impurities and dry at about 110°. Suspend 1 g. of the dry salt in 100 cc. of benzene and provide the flask with a reflux condenser. Boil until solution is obtained. Possibly the product is a colloidal dispersion rather than a very perfect solution. It has been found that a very little sodium oleate mixed with the magnesium oleate rendered the emulsions more permanent. 

Physically, milk is a rather dilute emulsion combined with a colloidal dispersion in which the continuous phase is a solution. Its physical properties are similar to those of water but are modified by the concentration of solutes and by the state of dispersion of the other components. 

Ross. S.. and I.D. Mumson Colloidal Dispersions Suspensions. Emulsions, ami I films 2nd Edition. John Wiley Sons. Inc.. New Yolk. NY. 2U02,... 

SN1 and reactions Two varieties of nucleophilic substitution, with unimolecular and bimolecular ratedetermining stages, respectively, sol A colloidal dispersion of solid particles in a liquid, solid A rigid form of matter that maintains the same shape whatever the shape of its container, solid emulsion A colloidal dispersion of a liquid in a solid. Example butter, an emulsion of water in butterfat. solid solution A solid homogeneous mixture of two or more substances. 

Emulsions are colloidal dispersions of liquid droplets in another liquid phase, sometimes stabilized by surface active agents. Emulsions thus consist of a discontinuous phase, dispersed in a continuous phase. The most common types of emulsions are water-in-oil (W/O) in which oil is the continuous phase, and oil-in-water (OAV) in which water forms the continuous phase. However, this traditional definition of an emulsion is too narrow to include most food emulsions. For example, in foods the dispersed phase may be partially solidified, as in dairy products or the continuous phase may contain crystalline material, as in ice cream. It may also be a gel, as in several desserts. In addition to this, air bubbles may have been incorporated to produce the desired texture. 

When conventional surfactants are used in emulsion polymerization, difficulties are encountered which are inherent in their use. Conventional surfactants are held on the particle surface by physical forces thus adsorption/des-orption equilibria always exist, which may not be desirable. They can interfere with adhesion to a substrate and may be leached out upon contact with water. Surfactant migration affects film formation and their lateral motion during particle-particle interactions can cause destabilization of the colloidal dispersion. 

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