Emulsion factors influencing

The final factor influencing the stabiHty of these three-phase emulsions is probably the most important one. Small changes in emulsifier concentration lead to drastic changes in the amounts of the three phases. As an example, consider the points A to C in Figure 16. At point A, with 2% emulsifier, 49% water, and 49% aqueous phase, 50% oil and 50% aqueous phase are the only phases present. At point B the emulsifier concentration has been increased to 4%. Now the oil phase constitutes 47% of the total and the aqueous phase is reduced to 29% the remaining 24% is a Hquid crystalline phase. The importance of these numbers is best perceived by a calculation of thickness of the protective layer of the emulsifier (point A) and of the Hquid crystal (point B). The added surfactant, which at 2% would add a protective film of only 0.07 p.m to emulsion droplets of 5 p.m if all of it were adsorbed, has now been transformed to 24% of a viscous phase. This phase would form a very viscous film 0.85 p.m thick. The protective coating is more than 10 times thicker than one from the surfactant alone because the thick viscous film contains only 7% emulsifier the rest is 75% water and 18% oil. At point C, the aqueous phase has now disappeared, and the entire emulsion consists of 42.3% oil and 57.5% Hquid crystalline phase. The stabilizing phase is now the principal part of the emulsion. 

When emulsion techniques are used for microsphere preparation, a number of processing factors influences the final structure of the microspheres, e.g., the choice of solvents and surfactants, phase viscosity, the ratio of the dispersed to the continuous phase, mixing speed, processing temperature, and time. Micro-... 

Another parameter that influences the overall properties of the bulk emulsion is the physical state of the lipid droplets in an emulsion (17, 19, 28-31). Crystallization of lipid droplets in emulsions can be either beneficial or detrimental to product quality. Margarine and butter, the most common water-in-oil emulsions in the food industry, are prepared by a controlled destabilization of oil-in-water emulsions containing partly crystalline droplets. The stability of dairy cream to mechanical agitation and temperature cycling depends on the nature and extent of crystallization in milk-fat globules. It should be noted that because the density of the phases can change as crystallization occurs, the rate at which milkfat droplets cream can be altered as droplets solidify. Emulsion manufacturers should therefore understand which factors influence the crystallization and melting of emulsified substances, and be aware of the effect that droplet phase transitions can have on the properties of emulsions. 

Factors Influencing Emulsion Rheology A variety of factors determine the rheological properties of food emulsions. Some of the most important of these factors are highlighted below. 

The appearance of an emulsion is one of the most important factors influencing its perceived quality, as it is usually the first sensory impression that a consumer makes of a product (4, 111). A better understanding of the factors that determine emulsion... 

Whatever the specific formulation used, the final concentration of the surfactant is selected on the basis of the characteristics of the heavy-crude-oil-brine system and the conditions to which the emulsion will be subjected. The principal factor influencing the quantity of surfactant required is the length of the pipeline system in which the emulsion will be pumped. The concentration of surfactant based on the total emulsion may range from 200 to 5000 ppm, depending on specific system characteristics. 

The rheological properties of emulsions are influenced by a number of interacting factors, including the nature of the continuous phase, the phase volume ratio, and to a lesser extent, particle size distributions. A variety of products ranging from mobile liquids to thick semisolids can be formulated by altering the dispersed phase volume and/or the nature and concentration of the emulsifiers. For low internal phase volume emulsions, the consistency of the emulsion is generally similar to that of the continuous phase thus. 

Size Distribution of Droplets A factor influencing the rate of coalescence of the droplets is the size distribution. The smaller the range of sizes, the more stable the emulsion. Since larger particles have less interfacial surface per unit volume than smaller droplets, in macroemulsions they are thermodynamically more stable than the smaller droplets and tend to grow at the expense of the smaller ones. If this process continues, the emulsion eventually breaks. An emulsion with a fairly uniform size distribution is therefore more stable than one with the same average particle size having a wider distribution of sizes. 

The strongest films are formed under the most acidic conditions. Finally, the films least able to relax under reduced surface stress conditions were observed to form the most stable emulsions. They also found that components other than asphaltenes, such as alkanes (paraffin waxes), resins, and aged interfacially active components of relatively high H/C ratio (1 5), can also contribute to the stabilization of water-in-crude oil emulsions. They concluded that the state of solvation of asphaltenes in the oil phase plays an important role in their ability to stabilize emulsions, which may explain the indirect action of resins on emulsion stability. The temperature is also an important factor when it comes to the stability of crude oil emulsions, especially true when the wax content is relatively high. The most important factor influencing the water-in-crude oil emulsion stability at low temperature is the interaction at the water-oil interface between wax crystals and the heavy fractions of the crude. 

In such a system, the rate of oxidation is influenced by the emulsion composition (relative concentrations of substrate and emulsifier) and especially, by the partition of the emulsifier between the interface and the water phases. Other factors influencing lipid oxidation in emulsions are particle size of the oil droplets, the ratio of oxidizable to non-oxidizable compounds in the emulsion droplets, and the packing properties of the surface-active molecules. In addition, the amount and composition of the oil phase in an emulsion are important factors that influence oxidative stability, formation of volatiles, and partition of the decomposition products, between the oil and water phase. 

N. Erden. N. Celebi. Factors influencing relea.se of sulbuiamol sulphate from polydactide-co-glycolidel microspheres prepared by water-in-oil-in-water emulsion technique. Int. J. Pharm. 137 57-66, 1996. 

Our account of the aforesaid factors influencing the kinetics and mechanism of emulsion polymerization (in both presence and absence of an emulsifier) has enabled the inflnence of comonomers on the processes of formation of polymeric dispersions based on (meth)acrylates to be explained. Changes of some conditions of reaction have tnmed ont to affect the character of influence of other ones. For example, increasing the concentration of MAA at its copolymerization with MA at a relatively low initiation rate leads to a decrease in the rate and particle nnmber and to an increase in the coagnlnm amonnt. Bnt at high initiation rates, the nnmber of particles in the dispersion in the presence of MAA rises and their stability improves. The same effects were revealed for emnlsifier-free polymerization of bntylacrylate as well, when at high temperatnres its partial replacement by MAA results in better stabilization of the dispersion, an increase in the reaction rate and the nnmber of particles (whereas their decrease was observed in the presence of an emulsifier). 

Factors Influencing Free Radical Generation in Food Emulsions... 

Initially, this chapter will begin with a description of the major factors influencing the formation, physicochemical properties, and stability of oil-in-water emulsions, as this will facilitate the understanding of the influence of water soluble polymers on emulsion characteristics. The physicochemical basis of the surface activity and film forming properties of water soluble polymers will then be covered. Finally, the characteristics of some of the most important water soluble polymers used as emulsifiers in the food industry will be discussed. 

Effect of Internal Phase Composition. In addition to the factors mentioned above, the stability of the extracting emulsion is influenced significantly by the composition of the internal phase. Among the factors which play the greatest role in determining the stability are the pH and ionic strength of the internal phase and the presence of organic substances (7). 

The stability of emulsions is influenced by many factors, such as the dispersed phase particle size (the smaller the particles, the more stable the emulsion), the amount of dispersed phase (more stable emulsions are formed with small amounts of dispersed phase), the densities of both phases (emulsions are stable when the differences... 

For premix membrane emulsification, the factors influencing the emulsification results are the transmembrane pressure, repeated processing and the pore size of the membrane. Furthermore the composition of the emulsion, like disperse and continuous phase viscosity, emulsifier and emulsifier concentration have also an influence on the emulsification results [28-31]. 

From the above discussion it is evident that the following factors influence the free-radical emulsion polymerization of vinyl chloride... 

The critical capillary number is the capillary number value below which no oil drop breakup occurs [10]. Grace [10] indicated that file viscosity ratio X (see (21.2)— viscosity of disperse //d and continuous phase is a crucial factor influencing the critical capillary number, especially for simple shear flow. Armhruster [11] and later Jansen et al. [12] showed that for high concentrated systems the viscosity of the emulsion rje, has to be used instead of the viscosity of cmitinuous phase. 

Csoka I, Eros 1.1997. Stability of multiple emulsions I. Determination of factors influencing multiple drop breakdown. Int I Pharm 156 119-123. 

It may seem that due to the different mechanisms and factors influencing the stability of nanoemulsions it is not possible to know a priori which will be the behavior of a defined system. However, the growing knowledge about a great variety of systems and a wise use of this knowledge would allow the formulation of nano-emulsions with enough stability for the applications intended. 

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