Foam stability, effect

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. 

On the other hand, if the solution is too dilute, then the surface tension of the solution will approach that of the pure solvent, and then the restoring force, which is the difference between the surface tension of the clean surface (than of the pure solvent) and the equilibrium surface tension of the solution, will be too small to withstand the usual thermal and mechanical shocks. Thus, according to this mechanism, there should be an optimum concentration for maximum foaming in any solution producing transient foams. (In these solutions the foam stabilization effects are much less important than the foam-producing effects, and therefore the latter can be measured more or less independently of the former.) This maximum in the foam valume-concentration curve of solution producing transient foams has been well verified experimentally. 

Aramaki, K., Aratani, K., and Kunieda, H. (2005) Interfadal properties and foam stability effect of novel gemini-type surfactant in aqueous solutions./. Colloid Interface Sci., 291, 236-243. 

Wasan, D., Nikolov, A.D., Huang, D.D., Edwards, D.A. Foam stability effects of oil and film stratification, in Surfactant-Based Mobility Control, Progress inMiscible Flood Enhanced Oil Recovery (Smith, D.H., ed.), ACS Symposium Series 373, Washington DC, 1988, Chapter 7, p 136. 

Betaines and sulfobetaines are also known for their foam-stabilizing effect [81]. 

Uses Detergent, surface tension reducer for liq. or powd. laundry detergents, multiple use detergents, shampoo for vehicles, automotive, textile degreasers Features Exc. foam stabilizing effect even in the presence of hard water F>roperties Liq. R-co color 60 max. cloud pt. 55 C acid value 0.5 max. hydroxyl value 108-119 pH 6.0-8.0 HLB 12.1 Tordedogy SI. toxir can cause skin irritation F recaution Wear personal protection equipment... 

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]. 

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. 

Foams are thermodynamically unstable. To understand how defoamers operate, the various mechanisms that enable foams to persist must first be examined. There are four main explanations for foam stabiUty (/) surface elasticity (2) viscous drainage retardation effects (J) reduced gas diffusion between bubbles and (4) other thin-film stabilization effects from the iateraction of the opposite surfaces of the films. 

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). 

Foam behavior and foam stability are strongly dependent on the water hardness. With a water hardness of 0 ppm the foam behavior and foam stability of LAS improves as the molecular mass increases. This behavior is exactly the opposite at a water hardness of 300 ppm. From 100 ppm the optimum for the Cn homologs is obtained. With the same molecular mass, the foam consistancy of the homologs is highest when the content of 2- and 3-phenylalkanes is highest [187]. In terms of stability in hard water a higher 2-phenylalkane content has a positive influence. An increase in molecular mass has the effect of reducing the hard water stability [189-191]. 

FIG. 11 Hardness effect on foam stability of LAS homologs in a 24% LAS/6% AES/ 2% amide dishwashing liquid. Conditions 46°C, 0.05% concentration, Keen soil. (From Ref. 19.)... 

Experimental correlations have been established in a given LDL formulation between foam stability and interfacial tension [33]. For example, Fig. 15 shows the effect of increasing water hardness on plate washing performance of an LAS/AES blend. A small amount of Ca2+ ion helps substantially to stabilize the foam. Under the same conditions interfacial tension is also lowered substantially. The two curves show an inverse relationship where the minimum interfacial tension value corresponds to the optimum level of foam stability as measured by plate washing [33]. 

The results in Table 22 for a series of one atmosphere 75 °C foaming experiments indicate the effect of hydrophobe carbon number. The foam stability of C18 AS is greater than that of C16 AS in the absence of an oil phase, in the presence of decane, and in the presence of the decane-toluene mixture. The foam stability of C18 HAS is greater than that of C16 HAS in the absence of an oil phase. In the presence of decane and in the presence of the decane-toluene mixture, the foam stability of the C18 HAS is, if anything, slightly less than that of C16 HAS. This may have been the result of partitioning effects. 

Fig. 7 Stabilization effect of various xylan types isolated from beech wood (GXl and GX2), corn cobs (AGXl), rye bran (AXRl and AXR3), and corn hulls (AXCl and AXC2) on the protein (BSA) foam against thermal disruption foam volume before (V1) and after (V2) heating at 95 °C for 3 min [128]...

Figure 9. Stabilizing effect of methylcellulose on foams generated by a suspension of effervescent antacid granules containing magnesium trisilicate and aluminum hydroxide...

Figure 9 illustrates the stabilizing effect of methylcellulose on the foams generated by a suspension of effervescent antacid granules containing magnesium trisilicate and ammonium hydroxide. Samples 1 and 2 are identical, except for 0.01% of methylcellulose contained in sample 1. The foam in sample 1 (methylcellulose) is stable even after 5 minutes, while the sample without methylcellulose has virtually no foam after 30 seconds. 

Incomplete texturization or partial denaturation at temperatures below 60 °C significantly increased gel strength, but at 75 °C or above, complete loss of the gelling property resulted. Foam volume remained high up to 50 °C but decreased significantly (p < 0.05) above 75 °C. Foam stability followed the same pattern as foam volume, being very stable for an hour below 50 °C. On the contrary, Phillips et al. (1990) reported that WPI heated to 80 °C had little effect on foam stability. 

The primary factor controlling how much gas is in the form of discontinuous bubbles is the lamellae stability. As lamellae rupture, the bubble size or texture increases. Indeed, if bubble coalescence is very rapid, then most all of the gas phase will be continuous and the effectiveness of foam as a mobility-control fluid will be lost. This paper addresses the fundamental mechanisms underlying foam stability in oil-free porous media. 

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