Emulsion interfacial properties

Dickinson, E. (1999a). Caseins in emulsions interfacial properties and interactions. International Dairy Journal, 9, 305-312. 

The traditional view of emulsion stability (1,2) was concerned with systems of two isotropic, Newtonian Hquids of which one is dispersed in the other in the form of spherical droplets. The stabilization of such a system was achieved by adsorbed amphiphiles, which modify interfacial properties and to some extent the colloidal forces across a thin Hquid film, after the hydrodynamic conditions of the latter had been taken into consideration. However, a large number of emulsions, in fact, contain more than two phases. The importance of the third phase was recognized early (3) and the lUPAC definition of an emulsion included a third phase (4). With this relation in mind, this article deals with two-phase emulsions as an introduction. These systems are useful in discussing the details of formation and destabilization, because of their relative simplicity. The subsequent treatment focuses on three-phase emulsions, outlining three special cases. The presence of the third phase is shown in order to monitor the properties of the emulsion in a significant manner. 

Our goal is to develop a property-performance relationship for different types of demulsifiers. The important interfacial properties governing water-in-oil emulsion stability are shear viscosity, dynamic tension and dilational elasticity. We have studied the relative importance of these parameters in demulsification. In this paper, some of the results of our study are presented. In particular, we have found that to be effective, a demulsifier must lower the dynamic interfacial tension gradient and its ability to do so depends on the rate of unclustering of the ethylene oxide groups at the oil-water interface. 

S. Arditly, V. Schmitfi F. Lequeux, and F. Leal-Calderon Interfacial Properties in Solid-Stabihzed Emulsions. Eur. Phys. J. B 44, 381 (2005). 

Key Concepts of Interfacial Properties in Food Chemistry CASE STUDY LIPID OXIDATION OF EMULSIONS The case of lipid oxidation in an emulsified system is a perfect example to illustrate the importance of interfacial properties in food chemistry. The goal of this case study is not to completely describe the very complex mechanisms of lipid oxidation in emulsions. Indeed, many investigators over the past years have focused on this research area. Instead, the key interfacial parameters that influence lipid oxidation in emulsions are emphasized. 

In colloidal dispersions, a thin intermediate region or boundary, known as the interface, lies between the dispersed and continuous phases. Each of emulsions, foams, and suspensions represent colloidal systems in which interfacial properties are very important because droplets, bubbles, and particles can have very large interfacial areas. 

Example. An emulsion is a dispersion of one immiscible liquid in another. In most cases one of the liquids is aqueous and the other is in some sense, an oil. Emulsions are another kind of colloidal system in which interfacial properties are very important because emulsified droplets have a large interfacial area. Even a modest interfacial energy per unit area can become a considerable total interfacial energy to be reckoned with. 

Of course, interfacial tension lowering alone may not be sufficient to stabilize an emulsion, in which case other interfacial properties must be adjusted as well. These simple calculations do, however, show how important the interfacial properties can become when colloidal-sized species are involved, as in the case of emulsions. 

Caims, R.J.R. Grist, D.M. Neustadter, E.L. The effects of Crude Oil-Water Interfacial Properties on Water-Crude Oil Emulsion Stability in Theory and Practice of Emulsion Technology, Smith, A.L. (Ed.), Academic Press New York, 1976 pp. 135-151. 

The energy plotted in Figure 7 was obtained by multiplying the total area by the interfacial tension. Now if a small quantity of a surfactant was added to the water, possibly a few tenths of a percent, that lowered the interfacial tension to 0.35 mN/m, it would lower the amount of mechanical energy needed in the example by a factor of 100. From the area per molecule that the adsorbed emulsifying agent occupies, the minimum amount of emulsifier needed for the emulsion can also be estimated. In practice, lowering interfacial tension alone may not be sufficient to stabilize an emulsion, in which case other interfacial properties must be adjusted as well. These simple calculations do, however, show how important the interfacial properties can become when colloidal-sized species are involved, as in emulsions. 

Effect of Emulsion Characteristics. The flow of emulsions in porous media is affected by a large number of variables. This section describes the properties of emulsions, such as stability, quality, droplet size distribution, oil viscosity, water-oil interfacial properties, and their effect on its flow in porous media. 

Droplet size depends on a number of factors such as the type of oil, brine composition, interfacial properties of the oil-water system, surface-active agents present (added or naturally occurring), flow velocity, and nature of porous material. For the study of OAV emulsions, McAuliffe (9) varied emulsion droplet sizes and size distributions by increasing the sodium hydroxide concentration in the aqueous phase, as shown in Figure 10. Higher NaOH concentration neutralizes more of the surface-active acids in the crude oil and produces an emulsion that has droplets of smaller diameters and is also more stable. Emulsion droplet size distribution can also be varied by varying the concentration of a surfactant added to the crude oil, as shown in Figure 11. 

Micellar-polymer flooding and alkali-surfactant-polymer (ASP) flooding are discussed in terms of emulsion behavior and interfacial properties. Oil entrapment mechanisms are reviewed, followed by the role of capillary number in oil mobilization. Principles of micellar-polymer flooding such as phase behavior, solubilization parameter, salinity requirement diagrams, and process design are used to introduce the ASP process. The improvements in ""classicaV alkaline flooding that have resulted in the ASP process are discussed. The ASP process is then further examined by discussion of surfactant mixing rules, phase behavior, and dynamic interfacial tension. 

Underlining that BCO and Diesel oil are not miscible a third component must be added to obtain a stable emulsion. This third component is called emulsifier (or surfactant). It changes the interfacial properties (namely interaction potential between droplets) of the system avoiding (or delaying) the emulsion s breaking. 

The combination of chemical and electrical treatment has been reported (31). Compounds, used in this application, are chemicals that have a property of liberating free chlorine radicals, such as chlorinated oils, chlorocosane, chloramines, toluene, and hydrochlorites. Effects of chemicals on the breaking of petroleum have been investigated. The most general explanation is that the coalescence of the dispersed phase in emulsion resulted from both chemical reaction and physical effects of the chemicals, change the interfacial properties and facilitating droplet-droplet coalescence. 

One of the main objectives of this study has been to determine the effect of interfacial properties on coalescence, emulsion stability and oil recovery efficiency for various surfactant and caustic systems. We have recently reported (6, 19) that for a petroleum sulfonate system there is no direct correlation between rates of coalescence and interfacial tension or interfacial charge. However, a qualitative correlation has been found between coalescence rates and interfacial viscosities. 

Much research has been carried out on the chemical structural properties of pectin,8 9 particularly on the composition of the constituent sugars,10 the solution properties,11 the mechanism of gelation12 and the interfacial properties,13 but so far the emulsion-stabilizing properties of depolymerized pectin have received little attention.14... 

His research interests have included many aspects of colloid and interface science applied to the petroleum industry, including research into mechanisms of processes for the improved recovery of light, heavy, or bituminous crude oils, such as in situ foam, polymer or surfactant flooding, and surface hot water flotation from oil sands. These mostly experimental investigations have involved the formation and stability of dispersions (foams, emulsions, and suspensions) and their flow properties, elec-trokinetic properties, interfacial properties, phase attachments, and the reactions and interactions of surfactants in solution. 

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