Foaming Foam stability

The adsorbed layer at G—L or S—L surfaces in practical surfactant systems may have a complex composition. The adsorbed molecules or ions may be close-packed forming almost a condensed film with solvent molecules virtually excluded from the surface, or widely spaced and behave somewhat like a two-dimensional gas. The adsorbed film may be multilayer rather than monolayer. Counterions are sometimes present with the surfactant in the adsorbed layer. Mixed monolayers are known that involve molecular complexes, eg, one-to-one complexes of fatty alcohol sulfates with fatty alcohols (10), as well as complexes between fatty acids and fatty acid soaps (11). Competitive or preferential adsorption between multiple solutes at G—L and L—L interfaces is an important effect in foaming, foam stabilization, and defoaming (see DEFOAMERS). 

Bakery Solubility, emulsifying, gelation Foaming, foam stability, water binding, gluten modification... 

Imitation dairy Emulsifying, colloidal stability Solubility, foaming, foam stability... 

Zwitterionic and amphoteric surfactants contribute to the overall generation of foam, foam stability and foam quantity. Regardless of the type of amphoteric, a generalization can be made concerning the hydrophobic R group The total number of carbon atoms in the R group has a profound effect upon performance. 

Features High efficiency foaming/foam stabilization compat. with most thickeners, fillers, auxs. effective low usage levels Regulatory FDA 21CFR 175.105,175.300,176.170 Properties 40% act. 

Exerowa and co-workers [201] suggest that surfactant association initiates black film formation the growth of a black film is discussed theoretically by de Gennes [202]. A characteristic of thin films important for foam stability, their permeability to gas, has been studied in some depth by Platikanov and co-workers [203, 204]. A review of the stability and permeability of amphiphile films is available [205]. 

The foregoing is an equilibrium analysis, yet some transient effects are probably important to film resilience. Rayleigh [182] noted that surface freshly formed by some insult to the film would have a greater than equilibrium surface tension (note Fig. 11-15). A recent analysis [222] of the effect of surface elasticity on foam stability relates the nonequilibrium surfactant surface coverage to the foam retention time or time for a bubble to pass through a wet foam. The adsorption process is important in a new means of obtaining a foam by supplying vapor phase surfactants [223]. 

Foam separation Foam stability FoamulaR Focused ion beams Fodder radish Fog... 

Defoamers. Foam is a common problem in papermaking systems (27). It is caused by surface-active agents which are present in the pulp slurry or in the chemical additives. In addition, partially hydrophobic soHd materials can function as foam stabilizers. Foam can exist as surface foam or as a combination of surface foam and entrained air bubbles. Surface foam usually can be removed by water or steam showers and causes few problems. Entrained air bubbles, however, can slow drainage of the stock and hence reduce machine speed. Another serious effect is the formation of translucent circular spots in the finished sheet caused by permanently entrained air. 

The surface active properties of aHphatic amine oxides were discovered ia the 1930s and the wetting, detergent, emulsion, and foam stabilizing properties were published shortiy thereafter (42). However, the use of amine oxides was not significant until Procter and Gamble started usiag them ia household products around 1960 (43—46). 

Sweetness is primarily a function of the levels of dextrose and maltose present and therefore is related to DE. Other properties that increase with increasing DE value are flavor enhancement, flavor transfer, freezing-point depression, and osmotic pressure. Properties that increase with decreasing DE value are bodying contribution, cohesiveness, foam stabilization, and prevention of sugar crystallization. Com symp functional properties have been described in detail (52). 

Several nonoccupational health problems have been traced to cobalt compounds. Cobalt compounds were used as foam stabilizers in many breweries throughout the world in the mid to late 1960s, and over 100 cases of cardiomyopathy, several followed by death, occurred in heavy beer drinkers (38,39). Those affected consumed as much as 6 L/d of beer (qv) and chronic alcoholism and poor diet may well have contributed to this disease. Some patients treated with cobalt(II) chloride for anemia have developed goiters and polycythemia (40). The impact of cobalt on the thyroid gland and blood has been observed (41). 

In most cases, these active defoaming components are insoluble in the defoamer formulation as weU as in the foaming media, but there are cases which function by the inverted cloud-point mechanism (3). These products are soluble at low temperature and precipitate when the temperature is raised. When precipitated, these defoamer—surfactants function as defoamers when dissolved, they may act as foam stabilizers. Examples of this type are the block polymers of poly(ethylene oxide) and poly(propylene oxide) and other low HLB (hydrophilic—lipophilic balance) nonionic surfactants. 

Both high bulk and surface shear viscosity delay film thinning and stretching deformations that precede bubble bursting. The development of ordered stmctures in the surface region can also have a stabilizing effect. Liquid crystalline phases in foam films enhance stabiUty (18). In water-surfactant-fatty alcohol systems the alcohol components may serve as a foam stabilizer or a foam breaker depending on concentration (18). 

Bendure indicates 10 ways to increase foam stability (1) increase bulk liquid viscosity, (2) increase surface viscosity, (3) maintain thick... 

One useful method of aqueous defoaming is to add a nonfoam sta-bihzing surfac tant which is more surface-active than the stabilizing substance in the foam. Thus a foam stabilized with an ionic surfactant can be broken by the addition of a very surface-active but nonstabihzing sihcone oil. The sihcone displaces the foam stabilizer from the interface by virtue of its insolubility. However, it does not stabilize the foam because its foam films have poor elasticity and rupture easily. 

Ross, S. Mechanisms of Foam Stabilization and Antifoaming Action, Chem. Eng. Progr. 63, 9, (1967) p. 41. 

Lauric acid is the main fatty acid used for producing ethanolamides. Monoethanolamides are used primarily in heavy-duty powder detergents as foam stabilizers and rinse improvers. 

Somewhere in the middle are soy lecithin and sorbitan mono-laurate, which make good foam stabilizers in whipped cream and similar products. 

PEGs are often reacted with fatty acids to make detergents that have thickening and foam-stabilizing properties. When chemically combined with fatty acids from coconut oil, they make detergents such as PEG-5 cocamide, which is used in shampoos as a surfactant, emulsifier, and foam stabilizer. 

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