Surfactants foam stability

Uses Conditioner, vise, builder, foam stabilizer, surfactant in cosmetics... 

To frame a context for describing the mode of action of antifoams in later chapters, we are concerned here with the criteria that determine whether oils will emerge into gas-liquid surfaces and whether they will spread at those surfaces. Those criteria are not confined to consideration of thermodynamic stability alone. In reality metastable states can exist that have a profound effect on whether antifoam action occurs. Complexity also arises because spreading oil molecules can be partially solubilized in the foam-stabilizing surfactant monolayers present at the relevant gas-liquid surfaces. All of these aspects are reviewed here, thermodynamic criteria being... 

The reaction is run at <150°C in the presence of a small amount of foam-stabilizing surfactant, to give a cellular resin of apparent density <301b/ft (480 g//). 

Provided that the interfacial tension of the antifoam and the liquid is sufficiently high (leading to incompatibility), the antifoam droplet migrates to the interface (Fig. 19) where it replaces foam-stabilizing surfactants in the foam lamella and spreads. The antifoam is dewetted, which leads to a destabilization of the foam lamella and eventually to a rupture of the foam bubbles. 

The most important hydrophobic particles are hydrophobic silica, waxes, and metal soaps. Carriers are needed to transport the hydrophobic particles into the foam lamella and bring them into contact with the foam-stabilizing surfactant layer. 

Air entraining agents that may also be used include foams formed ex-situ, including stabilized foams from water and a fluorochemical surfactant (41). Fluorochemical foam stabilizing surfactants are well known in the art of fire fighting foams. 

Indeed emulsions are everywhere and find extensive applications in the food, pharmaceutical, and cosmetics industries. Emulsions arc highly complex multicomponent systems containing emulsifiers, foam stabilizers, surfactants, solubilizers, viscosity conditioners and numerous other compounds. About 80% of emulsion preparations in the market are of... 

Chem. Descrip. Polysiloxane-polyether copolymer Uses Foam stabilizing surfactant for mfg. of rigid PU foams, esp. in mfg. of appliances... 

Definition Mixt. of ethanolamlnes of fatty adds from almond oil Formula RCO-N(CH2CH20H)2, RCO- rep. fatty acids from almond oil Uses Conditioner, vise, builder, foam stabilizer, surfactant In cosmetics Almond amide propylbetaine. See Almondamidopiopyl betaine Almond amides, N,N-bis (2-hydroxyethyl)-. See Almondamide DEA Almond amides, N-[3-(dimethylamino) propyl], N-oxide. See Almondamidopro-pylamine oxide... 

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]. 

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). 

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. 

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. 

Cocamide DEA (or MEA or TEA) is used as a foaming agent, to make lather. The other surfactants generate a certain amount of suds, but this foaming agent is added to get the amount just right. In addition to its foam-stabilizing effects, it is also a viscosity booster—it s thick. 

Another foam stabilizing detergent is PEG-5 cocamide, which is also a surfactant and emulsifier. 

Dishwashing foam stability performance of an LAS-based light-duty liquid (LDL) is strongly affected by the carbon chain distribution, by water hardness, and, under some conditions, by phenyl isomer distribution. Foaming characteristics of C)2 phenyl isomer blends have been reported previously for conditions where LAS is the single anionic surfactant in the formulation (phosphate-built laundry powder) and the level of residual water hardness is low [30,31]. Under these conditions the internal phenyl isomers of C,2 LAS gave better foam performance than the 2-phenyl isomer. 

These higher foaming properties are very useful for such cosmetic formulations as shampoos, showerbaths, and so on. This is the same with the forming of fine bubbles and the improving of foam stability of other surfactants such as, for example, alkyl ether sulfates due to the combination with ether carboxylates [57,67-69] (Table 9). 

Foam cement is a special class of lightweight cement. The gas content of foamed cement can be up to 75% by volume. The stability of the foam is achieved by the addition of surfactants, as shown in Table 10-9. A typical foamed cement composition is made from a hydraulic cement, an aqueous rubber latex in an amount up to 45% by weight of the hydraulic cement, a latex stabilizer, a defoaming agent, a gas, a foaming agent, and a foam stabilizer [359,362]. Foamed high-temperature applications are based on calcium phosphate cement [257]. 

In addition to the mobility control characteristics of the surfactants, critical issues in gas mobility control processes are surfactant salinity tolerance, hydrolytic stability under reservoir conditions, and surfactant propagation. Lignosulfonate has been reported to increase foam stability and function as a sacrificial adsorption agent (392). The addition of sodium carbonate or sodium bicarbonate to the surfactant solution reduces surfactant adsorption by increasing the aqueous phase pH (393). 

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