Stability of emulsions and

ThF Tadros. Polymeric surfactants , stabilization of emulsions and dispersions. In E Desmond Goddard, JV Gruber, eds. Principles of Polymer Science and Technology in Cosmetics and Personal Care. New York Marcel Dekker, 1999, pp 73-112. 

Damodaran, S. (2005). Protein stabilization of emulsions and foams. Journal of Food... 

The study of surface rheology is useful in connection with the stability of emulsions and foams (Chapter 10) and the effectiveness of lubricants, adhesives, etc. 

Surfactants are used for stabilization of emulsions and suspensions against flocculation, Ostwald ripening, and coalescence. Flocculation of emulsions and suspensions may occur as a result of van der Waals attraction, unless a repulsive energy is created to prevent the close approach of droplets or particles. The van der Waals attraction Ga between two spherical droplets or particles with radius R and surface-to-surface separation h is given by the Hamaker equation,... 

Fine solid particles adsorb at interfaces and can provide long-term kinetic stability of emulsions and foams.1"5 For more effective stabilization the particles must be much smaller than the dispersed droplets.1,2 For the production of microemulsions, nano-sized particles are therefore of particular interest. 

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. 

Stability of Emulsions and Miniemulsions. The stability of emulsions and miniemulsions is determined by following, as a function of time, the variation of the emulsified volume at fixed temperatures between - lO C and + 50 C. 

Stabilizer is used to refer to any ingredient that can improve the stability of emulsions, and it may therefore be either an emulsifier or a thickening agent. 

For the emulsification mechanism to work, however, the interfacial films must be stable. Plus, higher interfacial viscosity increases the stability of emulsions and oil lamellae. Cooke et al. (1974) reported that their qualitative data indicated an increase in interfacial viscosity could increase oil recovery under certain conditions. Regardless, experiences tell us a low interfacial viscosity is needed for a higher recovery. 

Castor et al. (1981b) observed that the IFT in the alkaline flooding was on the order of 0.1 mN/m. Their capillary numbers of alkaline floods are presented in Figure 10.18. The capillary number of alkaline floods was about 100 times higher than the capillary numbers in waterfloods. The alkaline flooding results from Castor et al. show that the recovery efficiencies could be better correlated with the stability of emulsions and wettability alteration than with IFT of the systems. 

Their role in formation and stabilizing of emulsions and foams, and in stabilizing suspensions. These functions depend on the propensity of proteins to adsorb at most interfaces. These aspects are discussed in Chapters 10-13. 

A special case of nanoparticle self-assembly is the Janus particle. It was shown that Janus particles are considerably more active than homogeneous particles of comparable size and chemical nature and that the interfacial activity can be increased by increasing the amphiphilic character of the particles. Thus, the Janus particles show a significant advantage in the stabilization of emulsions and foams over homogeneous particles as they unify the Pickering concept and the amphiphilicity of a simple surfactant. 

The use of substances that due to their ability to form structural-mechanical barrier are capable of very strong stabilization of emulsions (and especially of concentrated ones), allows one to prepare many commercial emulsions that are used e.g. in emulsion polymerization [55], lubricantcooling liquids, etc. Such surfactants, and especially natural ones, are widely used in food and pharmaceutical applications [56-58]. These surfactants are, for instance, formed as a result of chemical reaction between dextrins and their derivatives (generated by thermal decomposition and partial oxidation of starch) and oils. 

The interfacial behavior of protein-surfactant complexes is important in several areas such as the stability of emulsions and foams and the adsorption of proteins and surfactants from their binary solutions onto solid surfaces. Of particular interest is the adsorption of the milk proteins /3-lactoglobulin and /3-casein at the oil-water interface in the presence of nonionic surfactants in relation to food emulsions [56-58] and foam stability [59]. The adsorption of gelatin at the air-water [52,53,60], oil-water [6], and solid-water [62] interfaces in the presence of surfactants has also been studied. Other studies reported include adsorption from aqueous solutions of lysozyme plus ionic surfactants at solid surfaces [63,64], /3-lactoglobulin plus SDS onto... 

First, let us consider thin-film systems such as emulsions at interfaces. An emulsion is a quasi-stable suspension of fine drops of one liquid dispersed in another liquid. Emulsions, together with microemulsions, can be found in technology, and in almost every part of the petroleum production and recovery process in reservoirs, produced at wellheads, in many parts of the refining process, and in transportation pipelines [1-4]. Understanding the chemistry involved in the stabilization of emulsions and in crude oil emulsions in particular is important both for economic and environmental reasons. The presence of water in oil (w/o) and oil in water (o/w) results in several costly byproducts, such as corrosion, scale, and dissolved metals. Water-in-crude oil emulsions are responsible for the enormous increase in the viscosity of the crude oils produced in reservoirs. Transportation of the viscous crude oil through pipelines is difficult and adds to the cost of production of the oil. With increasing... 

The stability of emulsions and the concentration of the interfacially active fractions at the interface between oil and water are strongly affected by the properties of the oil phase when the interfacially active fiuctions are oil soluble (6). Li et al. showed that the increase of the aromaticity of the... 

Generally, the asphaltene fractions from most crude oils give a high stability of emulsions and flic resin fractions... 

Much effort has been devoted to discovering and understanding topological defects in nematic phases, for instance, by controlling the stability of emulsions and interaction between colloidal particles in the elastic ocean of nematic LCs [30,31]. In comparison, little attention has been paid to smectic LCs primarily because... 

Most discussions of surfactants in solution concern themselves with relatively low concentrations so that the system contains what may be called simple surfactant species such as monomers and their basic aggregates or micelles. Before entering into a discussion of micelles, however, it is important to know that although they have been the subject of exhaustive studies and theoretical considerations, they are only one of the several states in which surfactants can exist in solution. A complete understanding of surfactants requires a knowledge of the complete spectrum of possible states of the surfactant, including liquid crystalline phases, which can be important in the stabilization of emulsions and foams, as well in other areas. 

Sodium stearoyl lactylate is also used as an emulsifier in food emulsions such as icings, fillings, toppings and coffee whiteners. It is especially recommended for improving freeze-thaw stability of emulsions and foams. 

The unique density dependence of fluid properties makes supercritical fluids attractive as solvents for colloids including microemulsions, emulsions, and latexes, as discussed in recent reviews[l-4]. The first generation of research involving colloids in supercritical fluids addressed water-in-alkane microemulsions, for fluids such as ethane and propane[2, 5]. The effect of pressure on the droplet size, interdroplet interactions[2] and partitioning of the surfactant between phases was determined experimentally[5] and with a lattice fluid self-consistent field theory[6]. The theory was also used to understand how grafted chains provide steric stabilization of emulsions and latexes. 

As a consequence of the pressure difference across a curved interface, such an interface will resist deformation by exerting an external force. The larger this pressure difference is, the larger the resistance is. Therefore, smaller drops or bubbles are less easily deformable than larger ones. This phenomenon is relevant for the preparation and stability of emulsions and foams (see Chapter 8). 

Studying monolayers provides information on the orientation and association of the amphiphiles at interfaces. This information may also be useful for understanding self-assembled structures of such amphiphilic compounds (Chapter 11) as well as the role they play in the formation and stabilization of emulsions and foams (Chapter 18). 

The coupling of the motions of the interface and the adjacent bulk phase are of great importance for the stability of emulsions and foams. This will be further discussed in Chapter 18. 

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