Foam half-life

Surfactant Substrate olefin (% branching) Unsulfonated organic material (wt %)b Foam half-life (min)... 

Despite having a greater average carbon number than AOS 1618, IOS 1720 exhibits a lower foam half-life, 9.4 min as compared with 26.6 min (Table 23). The most probable cause of this behavior is the lower linearity of IOS 1720 its parent olefin was 22% branched, vs. <4% for the parent olefin of AOS 1618 with all other chemical structure features being the same. 

Figure 10. Foam half-life measurements of foam stability and foam height measurements of foaminess versus dilatational elasticity for aqueous foams stabilized by a-olefin sulfonates. (Reproduced from reference 22 Copyright 1986 American Chemical Society.)...

Table I shows the initial foam height, h°, and the foam half-life, rl/2, in the presence of different types of antifoams. The oil alone has low, foam-breaking efficiency (high initial foam height and half-life), the hydro-phobic particles alone are more effective, and the mixed type of agent is much better antifoam. The synergism between the oil and the hydrophobic solids is a general phenomenon. It generally occurs independently from the nature of the nonpolar oil (silicone or hydrocarbon oil) and the nature of the surfactant solution (anionic, cationic, or nonionic) (86, 88).

Note DMPS-5X is poly(dimethylsiloxane) (silicone) oil with 50-cSt viscosity T-500 and Tullanox-500 (Tulco Co.) are hydrophobic silica with 0.2-/xm particle size. The surfactant solution is 0.06 M SDS. hf° is the initial foam height, and r1/2 is the foam half-life. 

Figure 34. Effect of the solid concentration in mixed antifoams on the foam half-life Key + oil was DMPS-2C (200 cP) and solid was T-...

The static stability of a foam refers to the ability of the foam to resist bubble breakdown. The foam s static stability can be quantified by measuring its half-life. This is the time required at static conditions for the foam to drain half of its liquid volume. As parameters such as type of stabilizer, containment pressure, or foam generation process change, the stability will also change. Foam half-life is not a direct measurement of stability. Variations of foam stability will occur under different conditions. 

Surfactants play an important role in the formation and stability of foams. Investigators have determined foam stability by measuring the half-life (e.g. t 2) the foam. Half-life is the time required to reduce foam voLume to half of its initial value. It has been demonstrated that the foam stability (i.e.half-life) decreased with increasing temperature, whereas the foaminess of the surfactant solution increased with temperature. It is likely that these properties of foam depend on the molecular structure and concentration of the surfactant at the gas/liquid interface. Comparison of the results of static foam stability with that of the dynamic behavior of foam in porous media revealed that the foam stability is not required for efficient fluid displacement or a decrease in the effective air mc >ility in a porous medium. Moreover, the ability of the surfactants to produce in-situ foam was one of the important factors in the displacement of the fluid in a porous medium. 

SURFACTANTS FOAM VOILME, ml FOAM HALF-LIFE, min. 

Foam stability was evaluated using the parameter of half-life. Determined by visual observation is the foam half-life, i.e., the time for the foam height to reduce to 50% of its initial value. Time of the foam destruction was fixed by timer. 

Reeord the foam half-life as the time required for drainage of 50 ml of water in the bottom of the eylinder, as measured at the point when the meniseus rises above the 50 ml graduate. 

FIGURE 4.12 Foam half-life time of 0.05 wt.% sodium caseinate solutions as function of mean drop diameter of soybean oil. (From Prins, A. Theory and practice of formation and... 

Several minutes after foam generation has ceased, a process of foam collapse commences with these systems. A plot of the time for onset of that collapse for each alkane is shown in Figure 4.30. The foam is seen to be intrinsically unstable. In the case of undecane and the higher alkanes, the collapse commences at the same time as the foam in the absence of the alkanes as indicated in the figure. In the case of the lower alkanes, foam collapse commences much earlier—after a couple of minutes with hexane through to 6 min for decane, for example. A plot of foam half-life... 

FIGURE 4.31 Effect of 5 vol.% emulsified alkanes on foam half-life of a saline solution of 3.8 mM AOT. (Adapted from Aveyard, R., Binks, B.R, Fletcher, P.D.I., Peck, T., Garrrett, P.R., JCS Faraday Trans., 89, 4313, 1993. Reproduced by permission of The Royal Society of Chemistry.)... 

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