Crystallization in emulsions

FIG. 11. Transmission electron micrographs of freeze fractured oily droplets dispersed (a) in a hexagonal and (b) in a cubic liquid crystalline phase, bar 100 nm. From Mueller-Goymann, C., Liquid crystals in emulsions, creams and gels, containing ethoxylated sterols as surfactant, Pharm. Res. 1 154-158 (1984). 

Lopez, C., Lesieur, P., Keller, G., Ollivon, M. 2001a. Crystallization in emulsion application to thermal and structural behaviour of milk fat. In, Crystallization and Solidification Properties of Lipids (N. Widlak, R. Hartel, S. Narine, eds.), pp. 190-199, AOCS Press, Champaign, IL. 

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. 

Mileller-Goymann, C. Liquid crystals in emulsions, creams and gels, containing ethoxylated sterols as surfactant. Pharm. Res. 1984,1, 154-158. 

Crystallization in Emulsion Application to Thermal and Structural Behavior of Milk Fat... 

Studies of crystallization in emulsions and microemulsions are part of a new area of materials research, the aim of which is to produce advanced inorganic, organic, and inorganic-organic composite materials with well-defined properties. The research has been inspired by biomineralization, i.e., the strategies that living organisms use to form their skeletons or store minerals for various purposes. 

For example, Razumovsky and Damodaran [152] examined the potential thermodynamic incompatibility of various proteins at the air/water interface. In such systems, what would the role of intervening fat crystals be Part of the solution lies in determining phase continuity and the interplay of phase behavior and kinetics along with potential thermodynamic incompatibility of the various components [153]. In so doing, one could predict the behavior of particle systems in which individual particles have different properties (size, shape, and interactions) [145]. Therefore, the long-term challenge of determining the true extent of the role of fat crystals in emulsions is to combine the thermodynamics and physics of structure formation processes and the influence of individual components. 

For the latter purpose, dissolve the crystals in hot ethanol, and then add water drop by drop to the well-stirred solution until a line emulsion just appears then add more ethanol, also drop by drop, until the emulsion just redissolves. ow allow the solution to cool spontaneousK if the emulsion reappears, add a few drops of ethanol from time to time in order to keep the solution clear. Finally the o-nitrophenol separates in crystals, and the well-stirred mixture may now be cooled in ieewvater until crystallisation is complete. Filter, drain and diy either in an atmospheric desiccator, or by pressing between drying-paper. 

In the manufacture of explosives, sodium nitrate is used mainly in blasting agents. In slurries and emulsions, sodium nitrate improves stabiUty and sensitivity. It also improves the energy balance because sodium nitrate replaces water, so that more fuel can be added to the formulation. Sodium nitrate reduces crystal size of slurries, which in turn increases detonating speed. In dynamites sodium nitrate is used as an energy modifier. Typical content of sodium nitrate is 20—50 wt % in dynamites, 5—30 wt % in slurries, and 5—15 wt % in emulsions. Sodium nitrate is used also in permissible dynamites, a special type of dynamite for coal (qv) mining. 

In the simplest emulsions just described, the final separation is into two Hquid phases upon destabilization. The majority of emulsions are of this kind, but in some cases the emulsion is divided into more than two phases. One obvious reason for such a behavior is the presence of a material that does not dissolve in the oil or the water. One such case is the presence of soHd particles, which is common in emulsions for food, pharmaceuticals, and cosmetics. Another less trivial reason is that the surfactant associates with the water and/or the oil to form a colloidal stmcture that spontaneously separates from the two hquid phases. This colloidal stmcture may be an isotropic Hquid or may be a semisoHd phase, a Hquid crystal, with long-range order. 

The detection of Hquid crystal is based primarily on anisotropic optical properties. This means that a sample of this phase looks radiant when viewed against a light source placed between crossed polarizers. An isotropic solution is black under such conditions (Fig. 12). Optical microscopy may also detect the Hquid crystal in an emulsion. The Hquid crystal is conspicuous from its radiance in polarized light (Fig. 13). The stmcture of the Hquid crystalline phase is also most easily identified by optical microscopy. Lamellar Hquid crystals have a pattern of oil streaks and Maltese crosses (Fig. 14a), whereas ones with hexagonal arrays of cylinders give a different optical pattern (Fig. 14b). 

Sodium carboxymethylcellulose is acceptable for use in food, and is employed in a variety of foodstuffs. It is used to prevent formation of ice crystals in ice creams to control the consistency of cheese spreads to stabilise the emulsions needed in salad creams and to thicken toothpaste. 

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. 

Other detection modes in bright CL or BL reactions are multichannel detectors, which provide simultaneous detection of the dispersed radiation and produce a permanent image of a wide area. Photographic films or plates are emulsions that contain silver halide crystals in which incident photons produce stable clusters of silver atoms within the crystals. Internal amplification is provided in the development process by an electron donor that reduces the remaining silver ions to silver atoms within the exposed crystals. A complexing agent is used to remove the... 

The two main assumptions underlying the derivation of Eq. (5) are (1) thermodynamic equilibrium and (2) conditions of constant temperature and pressure. These assumptions, especially assumption number 1, however, are often violated in food systems. Most foods are nonequilibrium systems. The complex nature of food systems (i.e., multicomponent and multiphase) lends itself readily to conditions of nonequilibrium. Many food systems, such as baked products, are not in equilibrium because they experience various physical, chemical, and microbiological changes over time. Other food products, such as butter (a water-in-oil emulsion) and mayonnaise (an oil-in-water emulsion), are produced as nonequilibrium systems, stabilized by the use of emulsifying agents. Some food products violate the assumption of equilibrium because they exhibit hysteresis (the final c/w value is dependent on the path taken, e.g., desorption or adsorption) or delayed crystallization (i.e., lactose crystallization in ice cream and powdered milk). In the case of hysteresis, the final c/w value should be independent of the path taken and should only be dependent on temperature, pressure, and composition (i.e.,... 

This colorant is produced in the USA, where it also plays a minor role on the market. Its shade is a reddish yellow. P.Y.60 is used in trade sales paints and in emulsion paints. Poor resistance to organic solvents, lack of overcoating fastnesss, and a lightfastness that deteriorates rapidly with the degree of reduction with Ti02 are reasons for the limited commercial interest in this pigment. Crystal data are published by A. Whitaker [12],... 

Partial Coalescence in Emulsions Comprising Partially Crystallized Droplets 167... 

M. A.J.S. van Boekel and P. Walstra Stability of Oil-in-Water Emulsions with Crystals in the Dispersed Phase. Colloids Surfaces 3, 109 (1981). 

Opacifiers. Opaque shampoos are produced by incorporating high melting, wax-like, dispersible materials into their preparation. Some of these materials crystallize in such a fashion that they effect a pearlescence in the product. Opacifying agents found in shampoos include the glycol mono- and diesters, higher fatty alcohols such as cetyl and stearyl forms, stearate soaps, and latex copolymer emulsions. 

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