Interfacial tension foams

Wang, D.-M., Cheng, J.C., Yang, Z.-Y, Li, Q., Wu, W.-X., Yu, H.-Y., 2001a. Successful field test of the first ultra-low interfacial tension foam flood. Paper SPE 72147 presented the SPE Asia Pacific Improved Oil Recovery Conference, Kuala Lumpur, 6-9 October. 

Thus, adding surfactants to minimize the oil-water and solid-water interfacial tensions causes removal to become spontaneous. On the other hand, a mere decrease in the surface tension of the water-air interface, as evidenced, say, by foam formation, is not a direct indication that the surfactant will function well as a detergent. The decrease in yow or ysw implies, through the Gibb s equation (see Section III-5) adsorption of detergent. 

The Spreading process is governed by the spreading coefficient S defined as in equation 4 (30) where c is the surface tension of the foaming medium, C the surface tension of the defoamer, and C. the interfacial tension between them. 

Foam Production This is important in froth-flotation separations in the manufac ture of cellular elastomers, plastics, and glass and in certain special apphcations (e.g., food products, fire extinguishers). Unwanted foam can occur in process columns, in agitated vessels, and in reactors in which a gaseous product is formed it must be avoided, destroyed, or controlled. Berkman and Egloff (Emulsions and Foams, Reinhold, New York, 1941, pp. 112-152) have mentioned that foam is produced only in systems possessing the proper combination of interfacial tension, viscosity, volatihty, and concentration of solute or suspended solids. From the standpoint of gas comminution, foam production requires the creation of small biibbles in a hquid capable of sustaining foam. 

Detergency may be defined as the removal of dirt from solid surfaces by surface chemical means [29], and may be related to several surfactant properties, including wetting and rewelting ability, foam generation, and surface and interfacial tension. It has long been observed... 

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]. 

FIG. 16 Effect of LAS/AES ratio on dishwashing foam stability and interfacial tension. Conditions 46°C, 0.05% concentration, 50 ppm hardness, Keen soil. (From Ref. 33.)... 

Closely akin to the subject of emulsions is the field of foams, mentioned only in passing. The two fields are similar, in that their properties both depend on surface effects, changes in interfacial tension, electrolyte composition, and manner of preparation. 

Determining the interfacial tension between the foaming solution and the oil... 

Yo F is the foaming solution-oil interfacial tension and Yq is the surface tension of the oil. 

Spreading Coefficient. The spreading coefficient is defined as the difference of the surface tension of the foaming medium cry, the surface tension of the defoamer aj, and the interfacial tension of both materials a /. 

At a given NaCI concentration, an increase in temperature resulted in an increase in interfacial tension. In contrast, for a narrow range of CaCI concentrations, interfacial tensions decreased with increasing temperatures. Changes of the amphiphile at the oil/water interface accounted for some of the experimental observations. Since the extent of oil desaturation is dependent on interfacial tension, the tension data could be used to assess the ability of surfactants to reduce oil saturations in the reservoir for application of surfactants and foams to thermal recovery processes. 

The interfacial tension results reported in this paper are part of a study to examine the benefits of using commercial foam-forming surfactants with steam-based processes for obtaining additional oil recovery. Low interfacial tension at elevated temperatures is needed to reduce residual oil saturation and to allow foams to form, or enhance their performance. 

The complex interfacial dilational modulus ( ) is a key fundamental property governing foam and emulsion stability. It is defined as the interfacial tension increment (da) per unit fractional interfacial area change (dA/A) i.e.,... 

Although silicone oils by themselves or hydrophobic particles (e.g., specially treated silica) are effective antifoams, combinations of silicone oils with hydrophobic silica particles are most effective and commonly used. The mechanism of film destruction has been studied with the use of surface and interfacial tensions, measurements, contact angles, oil-spreading rates, and globule-entering characteristics for PDMS-based antifoams in a variety of surfactant solutions.490 A very recent study of the effect of surfactant composition and structure on foam-control performance has been reported.380 The science and technology of silicone antifoams have recently been reviewed.491... 

During the past few years, the determination of the interfacial properties of binary mixtures of surfactants has been an area in which there has been considerable activity on the part of a number of investigators, both in industry and in academia. The Interest in this area stems from the fact that mixtures of two different types of surfactants often have interfacial properties that are better than those of the individual surfactants by themselves. For example, mixtures of two different surface-active components sometimes reduce the interfacial tension at the hydrocarbon/water interface to values far lower than that obtained with the individual surfactants, and certain mixtures of surfactants are better foaming agents than the individual components. For the purpose of this discussion we define synergism as existing in a system when a given property of the mixture can reach a more desirable value than that attainable by either surface-active component of the mixture by itself. 

Kinsella (13, 14) summarized present thinking on foam formation of protein solutions. When an aqueous suspension of protein ingredient (for example, flour, concentrate, or isolate) is agitated by whipping or aeration processes, it will encapsulate air into droplets or bubbles that are surrounded by a liquid film. The film consists of denatured protein that lowers the interfacial tension between air and water, facilitating deformation of the liquid and expansion against its surface tension. 

Emulsions and foams are two other areas in which dynamic and equilibrium film properties play a considerable role. Emulsions are colloidal dispersions in which two immiscible liquids constitute the dispersed and continuous phases. Water is almost always one of the liquids, and amphipathic molecules are usually present as emulsifying agents, components that impart some degree of durability to the preparation. Although we have focused attention on the air-water surface in this chapter, amphipathic molecules behave similarly at oil-water interfaces as well. By their adsorption, such molecules lower the interfacial tension and increase the interfacial viscosity. Emulsifying agents may also be ionic compounds, in which case they impart a charge to the surface, which in turn establishes an ion atmosphere of counterions in the adjacent aqueous phase. These concepts affect the formation and stability of emulsions in various ways ... 

In milk, the important interfaces are those between the liquid product and air and between the milk plasma and the fat globules contained therein. Studies of the surface tension (liquid/air) have been made to ascertain the relative effectiveness of the milk components as depressants to follow changes in surface-active components as a result of processing to follow the release of free fatty acids during lipolysis and to attempt to explain the foaming phenomenon so characteristic of milk. Interfacial tensions between milk fat and solutions of milk components have been measured in studies of the stabilization of fat globules in natural and processed milks. 

In the related field of foam stability, De Vries (D3) has performed some very interesting studies. He suggests that the formation of a hole in the separating film and also the first expansion of this hole requires an increase of free energy. This activation energy, which must be supplied in order to make expansion possible, is proportional to the square of the film thickness and to the interfacial tension. The chance that this activation energy is indeed supplied is then described by a Boltzmann distribution function. 

These agents may operate via a number of mechanisms, but the most common ones appear to he those of entry and/or spreading. The defoamer must first of all he insoluble in the foaming liquid for these mechanisms to function. Second, the surface tension of the defoamer must be as low as possible. The interfacial tension between defoamer and foamer should be low. but not so low that emulsification of the defoamer may occur. Third, the defoamer should be dispersible in the foaming liquid. It was first shown in I fM8 that thermodynamically the entry of the defuamcr droplet into a bubble surface occurs when the entering coefficient has a positive value. The physics of bubbles is described in entry on Foam. 

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