Pseudoemulsion film stability

The thin liquid films bounded by gas on one side and by oil on the other, denoted air/water/oil are referred to as pseudoemulsion films [301], They are important because the pseudoemulsion film can be metastable in a dynamic system even when the thermodynamic entering coefficient is greater than zero. Several groups [301,331,342] have interpreted foam destabilization by oils in terms of pseudoemulsion film stabilities [114]. This is done based on disjoining pressures in the films, which may be measured experimentally [330] or calculated from electrostatic and dispersion forces [331], The pseudoemulsion model has been applied to both bulk foams and to foams flowing in porous media. 

Schramm and Novosad (76), Manlowe and Radke (77), and Hanssen and Dalland (80) also concluded that the pseudoemulsion film stability is a controlling factor in the stability of three-phase foams within porous media. 

Correlation between Pseudoemulsion Film Stability and Improved Oil Recovery. As the pseudoemulsion film controls the stability of bulk foams, it plays an important role also in the stability of foams in porous media containing crude oil. 

Nikolov et al. (1) were the first to find a direct correlation between pseudoemulsion film stability and crude oil displacement efficiency in... 

Wasan and co-workers (48, 50, 51) have found pseudoemulsion film stability to be influenced by micelle structuring effects, Marangoni surface effects, and the presence of oil droplets, (see the discussion in Chapter 2) They have also found that in some systems, the emulsification and imbibition of oil can actually stabilize foams. Manlowe and Radke s results (25) were interpreted in terms of pseudoemulsion film stabilities depending mainly on electrostatic and dispersion forces. Undoubtedly, interfadal viscosity could also be important. 

FIGURE 4.32 Effect of chain length of alkanes on half-life of single foam films prepared from 5 vol.% emnlsions of the oils in saline solution of 3.8 mM AOT ( ) and hatf-Ufe of single drops of alkane under air-solution surface as an indication of pseudoemulsion film stability ( ) (Reprinted from Adv. Colloid Interface ScL, 48, Aveyaid, R., Binks, B.R, Fletcher, P.D.I., Peck, T.G., Rutherford, C.E., 93. Copyright 1994, with permission from Elsevier.)... 

Effect of Stratified Layers of Polymer Latex Particles ON Foam and Pseudoemulsion Film Stability... 

A similar comparison of values of F with pseudoemulsion film stability is shown in Table 9.2, but using mixtures of hexadecane and hydrophobed silica. The usual antifoam synergy is observed regardless of the presence or absence of the latex polymer. No evidence of enhanced pseudoemulsion stability, due to the presence of the... 

The study of the behavior of this pseudoemulsion film with curvature is essential for understanding the role of spreading phenomena in three phase foam stability. 

As has been shown in the previous section, the stability of foam, emulsion and pseudoemulsion films manifest stratification phenomena, curvature phenomena and M arangoni phenomena. We will first discuss the microstructure of the thinning films due to micellar interactions, which we have observed through stratification phenomena. We will then discuss the observed behavior of the pseudoemulsion films with curvature and finally the role of Marangoni effects in the stabilization of the foam structure in the presence of oil. 

The interactions between an oil phase and foam lamellae are extremely complex. Foam destabilization in the presence of oil may not be a simple matter of oil droplets spreading upon foam film surfaces but may often involve the migration of emulsified oil droplets from the foam film lamellae into the Plateau borders where critical factors, such as the magnitude of the Marangoni effect in the pseudoemulsion film, the pseudoemulsion film tension, the droplet size and number of droplets may all contribute to destabilizing or stabilizing the three phase foam structure. 

Finally we should comment that it is necessary to employ in the calculation of the spreading coefficient (which is often used as a stability criterion) accurately measured values of the various tensions operative in the pseudoemulsion film to determine whether oil is spreading or nonspreading in the three phase foam structure. 

The interactions between foams and emulsified oil drops are discussed in the second part of this chapter. In the presence of emulsified oil, the mechanisms of foam stability are more complex than without oil. The mechanism of foam stability in the presence of oil drops is shown to be determined by the stability of the pseudoemulsion film. When the pseudoemulsion film is stable, the oil drops enhance the foam stability when the film is unstable, the oil acts as an antifoam (defoamer). In... 

In contrast, Figure 25 shows frames with the C16AOS solution. The oil drops drain from the films into the Plateau borders without entering or spreading, and the foam does not break. This observation was also in accordance with the observation that the typical oil configuration on the surface of C16AOS solution (Figure 23) was stable (thick or thin) pseudoemulsion film. These experiments clearly showed that the foam stability in the presence of emulsified oil is controlled by the stability of the pseudoemulsion film. 

The behavior of the pseudoemulsion film is controlled by mechanisms similar to foam films the interfadal rheological properties of the surfactant molecules at low surfactant concentrations and micellar ordering at high surfactant concentrations (i.e., much above the CMC). Not much above the CMC, both of these mechanisms can play a role in film thinning and stability. The stability of a thin pseudoemulsion film also depends on the van der Waals interactions between the phases at the two sides of the film, that is between air and oil, acting across the aqueous film. In a water pseudoemulsion film the Hamaker constant is generally negative, the van der Waals interactions are repulsive and stabilize the film. 

In the presence of micelles, solubilization of oil into the micelles of the solution takes place. The stability of aqueous pseudoemulsion film will be lower (faster film-thinning) in the presence of solubilized oil, similar to that shown in the stability of foam films, because oil solubilization... 

Lobo and Wasan (81) observed the drainage and stability of pseudoemulsion films from nonionic surfactant solutions (Enordet AE1215-30 ethoxylated alcohol) at concentrations much above the CMC. They observed that, for a 4 wt% surfactant system, the film thinned stepwise by stratification (Figure 27), in a fashion similar to the foam films from micellar solutions (Figure 14). Three thickness transitions were observed (81) at 4 wt% concentration with n-octane as oil, which was the same number of steps as observed by Nikolov et al. (54) in foam films at the same concentration. This observation on the micellar layering in the pseudoemulsion film confirms, again, the universality of the stratification phenomenon. 

Ride of the Pseudoemulsion Film in Antifoaming Action. The antifoaming efficiency strongly depends on the stability of the pseudoemulsion film. It must rupture in order for the drop, lens, or particle to enter the... 

The stability of pseudoemulsion film was studied directly in our laboratory, by forming such a film from a surfactant solution (0.06 M sodium dodecyl sulfate) on the tip of a capillary (Figure 33). The tip of the capillary, which was filled with antifoam oil, was covered with a small pseudoemulsion film from the surfactant solution. Then, the oil was slowly pushed out of the capillaiy. In this way, the area of the pseudoemulsion film and the capillary pressure was increased. The pseudoemulsion film between silicone oil containing no particles and air was relatively stable, and it did not rupture before the capillary pressure maximum, (i.e., hemispherical shape). However, when the oil contained hydrophobic silica particles, the film was much less stable. At high particle concentrations (1—6 wt%), the film ruptured shortly after it was formed, (i.e., at very low capillary pressures). 

Immersion Depth and Position of Antifoams. In addition to the stability of the pseudoemulsion film, several factors influence the efficiency of the various antifoams. 

The effect of oil on aqueous foam stability is controlled by the behavior of the pseudoemulsion films. In the previous sections, two extreme cases of the foam-oil interactions were shown foam stabilizing when the pseudoemulsion films are stable and antifoaming that is, fast foam rupture, when these films are very unstable. 

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