Foam dispersity definition

Classically, aerosols are particles or droplets that range from about 0.15 to 5 p.m ia size and are suspended or dispersed ia a gaseous medium such as air. However, the term aerosol, as used ia this discussion, identifies a large number of products which are pressure-dispensed as a Hquid or semisohd stream, a mist, a fairly dry to wet spray, a powder, or even a foam. This definition of aerosol focuses on the container and the method of dispensiag, rather than on the form of the product. 

The qualitative correspondence between the experimentally obtained foam dispersity vs. foam drainage rate and that of Eq. (5.60) can be seen in Fig. 5.19 [21]. The dispersity change was achieved by blowing air through sintered glass filters of definite pore radii. 

All the results presented so far give reason to conclude that the avalanche-like destruction of a foam column at definite temperature, pressure drop and foam dispersity, depends mainly on the equilibrium pressure reached. However, in order to establish the mechanism of action of the critical pressure drop, further studies of single foam films and foams are required. They should be performed under conditions that reveal the role of all elements of the foam (films, borders and vertexes) in the process of foam destruction. 

The initial expansion ratio and dispersity of polyhedral foams are related through the quantitative dependence, given by Eq. (4.9). There at Ap > 103 Pa the content of the liquid phase in the films can be neglected. Thus, the connection of the structure parameters n, a and r can be expressed by the simple relation in Eq. (4.10). It follows from it that under given foaming conditions a definite expansion ratio can be reached by changing the border pressure, foam dispersity and surface tension of the foaming solution. 

Definition and Classification of Foams. Colloidal species of any kind (bubbles, particles, or droplets), as they are visually defined, have at least one dimension between 1 and 1000 nm. Foams are a special kind of colloidal dispersion one in which a gas is dispersed in a continuous liquid phase. The dispersed phase is sometimes referred to as the internal (disperse) phase, and the continuous phase as the external phase. In practical occurrences of foams, the bubble sizes usually exceed the size limit given, as may the thin liquid-film thicknesses. Table II lists some simple examples of petroleum industry foam types. Solid foams, dispersions of gas in a solid, will not in general be covered in this chapter. A glossary of frequently encountered foam terms in the science and engineering of petroleum industry foams is given at the end of this volume. 

With foams, one is dealing with a gaseous state or phase of matter in a highly dispersed condition. There is a definite relationship between the practical application of foams and colloidal chemistry. Bancroft (4) states that adopting the very flexible definition that a phase is colloidal when it is sufficiently finely divided, colloid chemistry is the chemistry of bubbles, drops, grains, filaments, and films, because in each of these cases at least one dimension of the phase is very small. This is not a truly scientific classification because a bubble has a film round it, and a film may be considered as made up of coalescing drops or grains. ... 

Microscopy in Food Science is in an exciting state of flux. Traditional techniques of specimen preparation and observation will continue to give essential data on the structure of foods. However, the emphasis in the future will probably lie in the development of faster methods and in the quantification of individual components, both aiming at definition of structre /function relationships. This will be true of particulates as they relate to sensory scores and to the characterization of dispersed phases in emulsions and foams. At the same time, the use of microchemical methods should become more common as a means of... 

Although most colloidal dispersions are not thermodynamically stable, a consequence of the small size and large surface area in colloids, and of the presence of an interfacial film on droplets, bubbles or particles, is that dispersions of these species, having reasonable kinetic stability, can be made. That is, suspended droplets or particles may not aggregate quickly nor settle or float out rapidly and droplets in an emulsion or bubbles in a foam may not coalesce quickly. Many food and personal care product emulsions and suspensions, for example, are formulated to remain stable for months to years. It is crucial that stability be understood in terms of a clearly defined process, and one must consider the degree of change and the time-scale in the definition of stability. 

The correlation between the stability of single O/W emulsion films, single drops under oil/water interfaces and real emulsions found in [514,516] also deserves attention. As revealed in the beginning of this Section the correlation between emulsions and emulsion films was studied in various aspects and always provide information about stability of such systems. Model studies of emulsion systems are worth further development especially if the correlation films/real emulsion is done at definite conditions which are as close as possible in both cases, for example, at equal capillary pressure, film size, emulsion dispersity, etc., as it is done in the correlation foam films/foam (see Chapter 7). 

A more precise expression of the foaming and emulsifying ability involves the maximum volume of the interfacial area of emulsion drops, obtained under definite conditions from a unit volume of the dispersion medium [92]... 

Palytoxin is a white, amorphous, hydroscopic solid that has not yet been crystallized. It is insoluble in nonpolar solvents such as chlorophorm, ether, and acetone sparingly soluble in methanol and ethanol and soluble in pyridine, dimethyl sulfoxide, and water. The partition coefficient for the distribution of palytoxin between 1-butanol and water is 0.21 at 25°C based on comparison of the absorbance at 263 nm for the two layers. In aqueous solutions, palytoxin foams on agitation, like a steroidal saponin, probably because of its amphipathic nature. The toxin shows no definite melting point and is resistant to heat but chars at 300°C. It is an optically active compound, having a specific rotation of -i-26° 2° in water. The optical rotatory dispersion curve of palytoxin exhibits a positive Cotton effect with [a]25o being -i-700° and [a]2,j being +600° (Moore and Scheuer 1971 Tan and Lau 2000). 

The scaled surface area and its variation with d> are of crucial importance in the definition and evaluation of the osmotic pressure , H, of a foam or emulsion. We introduced the concept in Ref 37, where it was referred to as the compressive pressure , P. It has turned out to be an extremely finitful concept (22,27,38). The term osmotic was chosen, with some hesitation, because of the operational similarity with the more familiar usage in solutions. In foams and emulsions, the role of the solute molecules is played by the drops or bubbles that of the solvent by the continuous phase, although it must be remembered that the nature of the interaetions is entirely different. Thus, the osmotic pressure is denned as the pressure that needs to be applied to a semipermeable, freely movable membrane, separating a fluid/fluid dispersion from its continuous phase, to prevent the latter from entering the former and to reduce thereby the augmented surface free energy (Fig. 4). The membrane is permeable to all the components of the continuous phase but not to the drops or bubbles. As we wish to postpone diseussion of compressibility effects in foams until latter, we assume that the total volume (and therefore the volume of the dispersed phase) is held constant. 

Definition PEG ether of cetearyl alcohol Formula R(OCH2CH2)nOH, R = blend of cetyl and stearyl radicals, avg. n = 11 Properties Nonionic Toxicology TSCA listed Uses Solubilizer, emulsifier, dispersant for cosmetics and pharmaceuticals binder coating material for foam suppressant, enzymes, etc. dyeing auxiliaries in food-contact textiles... 

U n itex http //www. unitexchemical. com] Dicyclohexyl sodium sulfosuccinate CAS 23386-52-9 EINECS/ELINCS 245-629-3 Synonyms Sodium 1,4-dicyclohexyl sulfobutanedioic acid Sodium 1,4-dicyclohexyl sulfonatosuccinate Sodium dicyclohexyl sulfosuccinate Sodium 1,4-dicyclohexyl sulfosuccinate Succinic acid, sulfo-, 1,4-dicyclohexyl ester, sodium salt Definition Sodium salt of the diester of cyclohexyl alcohol and sulfosuccinic acid Empiricai C16H26O7S Na Properties Anionic Toxicoiogy TSCA listed Uses Dispersant, surfactant, emulsifier for modified S/B post additive to stabilize latex and promote adhesion pigment dispersant surfactant, foaming agent, hydrotrope in cosmetics emulsifier in food pkg. 

Definition Disodium salt of the half ester of nonoxynol-10 and sulfosuccinic acid Properties Anionic Toxicology TSCA listed Uses Emulsifier, solubilizer, wetting agent, surfactant, dispersant, foam booster/stabilizer, surf. tens, depressant in PVAc acrylic emulsions, paints, textile emulsions pad-bath additive in food-pkg. adhesives Regulatory FDA 21CFR 175.105 Trade Name Synonyms Aerosol A-103 [Cytec Ind. http //www.c ec.com, Cytec Ind. BV] Fizul... 

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