Aqueous foam

Commercial Disperse Azo Dyes. The first proposal to use insoluble dyes in suspension in an aqueous foam bath, ie, disperse dyes, to dye cellulose acetate was in 1921 (60). Commercialization of disperse dyes began in 1924 with the introduction of the Duranol dyes by British Dyestuffs Corporation (61) and the SRA dyes by British Celanese Company (62). In contrast to the acid monoazo dyes, derivatives of benzene rather than of naphthalene are of the greatest importance as coupling components. Among these components mono- and dialkylariifines (especially A/-P-hydroxyethyl-and A/-(3-acetoxyethylanifine derivatives) are widely used couplers. Nitrodiazobenzenes are widely used as diazo components. A typical example is CeUiton Scarlet B [2872-52-8] (91) (Cl Disperse Red 1 Cl 11110). 

Chlorine dioxide gas generated from chlorite has been used as a chemosterilizing agent substitute for ethylene oxide in medical appHcations (174,175). Aqueous foam compositions containing chlorine dioxide have also been developed for the sanitization of hard surfaces (176). 

AH these mechanisms except high bulk viscosity require a stabilizer in the surface layers of foam films. Accordingly, most theories of antifoaming are based on the replacement or modification of these surface-active stabilizers. This requires defoamers to be yet more surface active most antifoam oils have surface tensions in the 20 to 30 mN/m range whereas most organic surfactant solutions and other aqueous foaming media have surface tensions between 30 and 50 mN/m(= dyn/cm). This is illustrated in Table 3. 

Hydrophobic silica Finely divided silica in polydimethyl siloxane Aqueous foaming systems... 

Emulsifiers are essential in oil-water emulsion systems. For example, oU-in-water emulsifiers are used to promote the dispersion in aqueous foaming systems. 

Norman, E. C., Vapour suppression by aqueous foams, Chapter 2 in Hazardous and toxic materials, Fawcett, H. H. (ed.), New York, Wiley, 2nd edn., 1988... 

The use of aqueous foams to control fume or vapour release from reactive chemicals is discussed. An acid-resistant foam NF2 controlled fume emission from 35% and 65% oleum, and from titanium tetrachloride, but was not effective for sulfur trioxide and chlorosulfuric acid. An alcohol-resistant foam NF1 suppressed ammonia vapour emission by 80%, and Universal fire foam reduced evaporation of ethylene oxide, vinyl chloride and methanethiol, and reduced vapour emission of 1,3-butadiene by 60%. Safety aspects of foam blanketing are discussed [1]. Equipment and application techniques are covered in some detail [2],... 

V. Bergeron and C.J. Radke Equilibrium Measurements of Oscillatory Disjoining Pressures in Aqueous Foam Films. Langmuir 8, 3020 (1992). 

Measurements have been carried out on the excess tensions, equilibrium thicknesses, and compositions of aqueous foam films stabilized by either n-decyl methyl sulfoxide or n-decyl trimethyl ammonium-decyl sulfate, and containing inorganic electrolytes. 

Actually, avalanches of popping bubbles were put in evidence during the coarsening of bidimensional and three-dimensional aqueous foams (Ritacco et ah, 2007 Vandewalle et ah, 2001). How does the bubble raft behave at the surface of a flute poured with champagne Does a bursting... 

Foams and emulsions are other multiphase systems to which research on the application of NMR imaging is on-going. There are a great many practical uses of aqueous foams and emulsions in food, pharmaceuticals, and engineering. Understanding and particularly assigning specific functional roles to individual components in the foam has been severely... 

Chemical Defoamers The addition of chemical foam breakers is the most elegant way to break a foam. Effective defoamers cause very rapid disintegration of the foam and frequently need be present only in parts per million. The great diversity of compounds used for defoamers and the many different systems in which they are applied make a brief and orderly discussion of their selection difficult. Compounds needed to break aqueous foams may be different from those needed for aqueous-free systems. The majority of defoamers are insoluble or nonmiscible in the foam continuous phase, but some work best because of their ready solubility. Lichtman (Defoamers, 3d ed., Wiley, New York, 1979) has presented a concise summary of the application and use of defoamers. Rubel (Antifoaming and Defoaming... 

Foams may contain not just gas and liquid (and usually surfactant), but also dispersed oil droplets and/or solid particles. Figure 1.5 shows a practical aqueous foam that contains dispersed oil droplets within the foam lamellae. This can occur, for example, when a foaming solution is used for detergent action in a cleaning process (see Section 12.2) or when a foam is propagated through an underground oil reservoir as part of an enhanced oil recovery process (See Section 11.2.2). 

Figure 1.5 shows an example of an aqueous foam with emulsified and imbibed crude oil droplets residing in its plateau borders. Using a simple model the degree of emulsification and imbibition has been found to correlate quite well with foam sensitivity to oil for a wide variety of foams, oils, and conditions [114]. A limitation of emulsification/imbibition models is that they will only be important for foam lamellae that are thick enough to accommodate realistic emulsion droplet sizes. Typical foam lamellae in porous media appear to have thicknesses on the order of tens of nm [70,71,114,328],... 

Foams and emulsions may also be encountered simultaneously [114]. Figure 1.5 shows an example of an aqueous foam with oil droplets residing in its Plateau borders (see Section 5.6.7). In addition to containing gas, an aqueous phase, and an oleic phase, foams can also contain dispersed solid particles. Oil-assisted flotation of mineral particles provides one example (Chapter 10). Oil-sand flotation of bitumen provides another (Chapter 11). In the case of oil-sands flotation, an emulsion of oil dispersed in water is created and then further separated by a flotation process, the products of which are bituminous froths that may be either air (and water) dispersed in oil (from primary flotation) or air (and oil) dispersed in water (from secondary flotation). In either case, the froths must be broken and de-aerated before the bitumen can be upgraded to synthetic crude oil. (See Section 11.3.2). 

The removal of the gas phase from a dispersion. Example Some non-aqueous foams (made from bitumen or heavy crude oils) are very viscous and are de-aerated by processes such as contacting with steam in cascading froth, countercurrent steam-flow vessels. 

Wasan, D.T. Koczo, K. Nikolov, A.D. Mechanisms of Aqueous Foam Stability and Antifoaming Action With and Without Oil A Thin Film Approach in Foams, Fundamentals and Applications in the Petroleum Industry, Schramm, L.L. (Ed.), American Chemical Society Washington, DC, 1994, pp. 47-114. 

Choi, C.Y. Development and Evaluation of Aqueous Foam for Cold Protection in Greenhouses in Proc. Ann. ASAE Meeting ASAE ... 

DiMaio, L. R., and E. C. Norman. 1990. Continuing Studies of Hazardous Material Vapor Mitigation Using Aqueous Foams. Plant/Operations Progress, 5(3) 135. 

Although whey protein concentrates possess excellent nutritional and organoleptic properties, they often exhibit only partial solubility and do not function as well as the caseinates for stabilizing aqueous foams and emulsions (19). A number of compositional and processing factors are involved which alter the ability of whey protein concentrates to function in such food formulations. These include pH, redox potential, Ca concentration, heat denaturation, enzymatic modification, residual polyphosphate or other polyvalent ion precipitating agents, residual milk lipids/phospholipids and chemical emulsifiers (22). 

Obviously, this peculiarity can be explained with the decrease in the intermolecular attraction in emulsion films and the resulting increase in the barrier of the 11(h) isotherm (see Section 3.3.1). Hamaker s constant A for emulsion films is by a decimal order of magnitude lower than that of aqueous foam films and is within the range of 1.5-10-10 21 J depending on the surfactant kind and the nature of the organic phase [31]. It should be noted that in the... 

In the study of the mechanism of heterogeneous defoaming along with the spreading coefficients the so-called enter coefficient (destruction coefficient) is used to estimate the instability of aqueous foam films... 

However, the kinetic dependence of foam column decay proposed by Schwarz appears to be better grounded [8]. No attempts to relate the constants characterising the rate of foam column destruction with both physicochemical characteristics of the foaming solution and foam structure have been reported. The stepwise kinetics of decay of the foam column is typical for aqueous as well as non-aqueous foams. Manegold [32] points out that coarse foams decay in larger steps than finely disperse foams. 

Thermal insulators from frozen aqueous foams... 

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