Three-phase foam, stabilization

Three phase foam stability, as has been discussed by numerous authors is of great practical significanct (1-14). However, despite the recognized significance, the mechanisms by which oil affects foam stability are still under investigation. 

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. 

To establish a correlation between the interracial tension gradient measurements given above with three phase foam stability we used the qualitative Barch method for determining foam stability, due to the physicochemical difficulties in providing an accurate measure of three phase foam stability. 

These high stability foams correlate directly with the results based upon interfacial tension gradient measurements, confirming the significance of Marangoni phenomena (31) in three phase foam stability. 

Similar three phase foam stability tests have been performed for presence of Salem (light oil) and... 

Our objective in this study is to elucidate the complex phenomena occurring during the process of three phase foam thinning, to identify the interaction mechanisms between the oil droplets, the thinning foam film and the Plateau-Gibbs borders and the role of surface and interfacial tension gradients in foam stability, and to examine the implications upon crude oil displacement by foam in pourous media. 

Of course the Marangoni effect is not the only stabilizing factor in the three phase foam. Another critical factor is droplet size. Smaller droplet size is accomplished by lower interfacial tension, wherefore it is found that C AOS yields more stable foam... 

There appear then three primary mechanisms for stabilizing (or destabilizing) a three phase foam. The first derives from the micelle structuring in the film and depends directly upon surfactant concentration and electrolyte concentration. The second is a surface tension gradient (Marangoni) mechanism which relates to the short range intermolecular interactions and the rate of surface expansion. And the third is an oil droplet size effect which depends upon the magnitude of the dynamic interfacial tension. 

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. 

The stability of emulsion and foam films have also been found dependent upon the micellar microstructure within the film. Electrolyte concentration, and surfactant type and concentration have been shown to directly influence this microstructure stabilizing mechanism. The effect of oil solubilization has also been discussed. The preceding stabilizing/destabilizing mechanisms for three phase foam systems have been shown to predict the effectiveness of aqueous foam systems for displacing oil in enhanced oil recovery experiments in Berea Sandstone cores. 

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. 

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. 

Influence of Emulsion Film Stability. The stability of the emulsion drops inside three-phase foam systems has an influence on the foam stability. When the oil drops collect (flocculate) in the Plateau borders, the drops are compressed and give rise to the formation of emulsion films (Figures 1 and 2). If the emulsion films are stable, drops do not coalesce, and the foam stability is not affected. However, if these emulsion films are unstable, the oil drops coalesce in the Plateau borders and then, on further foam drainage, the large drops relocate, under the action... 

Phenomena at Liquid Interfaces. The area of contact between two phases is called the interface three phases can have only aline of contact, and only a point of mutual contact is possible between four or more phases. Combinations of phases encountered in surfactant systems are L—G, L—L—G, L—S—G, L—S—S—G, L—L, L—L—L, L—S—S, L—L—S—S—G, L—S, L—L—S, and L—L—S—G, where G = gas, L = liquid, and S = solid. An example of an L—L—S—G system is an aqueous surfactant solution containing an emulsified oil, suspended soHd, and entrained air (see Emulsions Foams). This embodies several conditions common to practical surfactant systems. First, because the surface area of a phase iacreases as particle size decreases, the emulsion, suspension, and entrained gas each have large areas of contact with the surfactant solution. Next, because iaterfaces can only exist between two phases, analysis of phenomena ia the L—L—S—G system breaks down iato a series of analyses, ie, surfactant solution to the emulsion, soHd, and gas. It is also apparent that the surfactant must be stabilizing the system by preventing contact between the emulsified oil and dispersed soHd. FiaaHy, the dispersed phases are ia equiUbrium with each other through their common equiUbrium with the surfactant solution. 

A closer relationship between foam stability and HLB has been reported for two- or three-phase systems surfactant solution-oil or oil-surfactant phase-water [60,109-111]. The effect of various parameters changing HLB on the stability of foams and emulsions has been studied in [111]. These were the concentration of amyl alcohol and sodium chloride, the number of the ethylene oxide groups in the molecule of the oxyethylated octylphenol. As a general parameter of HLB the authors used the surfactant affinity difference concept (SAD) which is an empirical generalised formulation. It measures the deviation from the optimum formulation for three phase behaviour. For anionic surfactants... 

Three-phase two-layer foam stabilized quick-breaking... 

Selectivity of the flotation process is determined by both selective hydrophobisation of mineral particles and conditions of their aggregation, stability and conditions of destruction of three-phase flotation foams. 

The interfacial behavior of block copolymers is of interest in several fields like stabilization of emulsions, foams, and wetting control [154]. Gerdes et al. [155] studied the wetting behavior of aqueous solutions of triblock copolymers on silica. The experimental approach was based on the use of a Wilhelmy force balance and direct images of contact angle. Their results show that the three-phase contact line advances in jumps over the surface when it is immersed at constant speed into the copolymer solution. Apparently the stick-slip spreading mechanism is the same as has been proposed for short chain cationic surfactants. 

---