Emulsion bulk properties, determination

The efficiency of any water-removal steps depends upon the size distribution of the dispersed water and the stability of the emulsion. Emulsion formation may be exacerbated by inappropriate pumping speed or other process variables. An evaluation of the chemical and physical factors that determine emulsion size distribution or emulsion bulk properties is essential to optimize emulsion breaking efficiency. 

Characterization of such emulsions therefore often involves three phases the water phase, the oil phase, and the solids. Complete characterization of an emulsion could therefore involve detailed chemical and physical analysis of all of the emulsion components, as well as any bulk properties that might be of interest (viscosity, density, etc.). This level of detail is clearly beyond the scope of this discussion. For the purposes of this chapter, emulsion characterization will be defined as the quantification of the phases present, the determination of the nature and size distribution of... 

Although surface phenomena determine the fundamental properties of emulsions in terms of size distributions and stability, the bulk properties or bulk compositions are the yardsticks by which plant operators and process personnel measure process efficiency. Accurate determination of the oil, water, and solids (if present) is therefore one of the most important aspects of emulsion characterization. 

Food scientists are interested in the colloidal properties of emulsions because of their influence on the overall quality and physicochemical properties (texture, stability, appearance, and taste) of products. The emulsion properties most important in determining the bulk properties of the... 

In normal conditions, PMMA is a hard transparent material. Molecular weight is the main property determinant. High molecular weight PMMA can be manufactured by free radical polymerization (bulk, emulsion, and suspension polymerisation). Bulk polymerization is used for cast semifinish products (sheet, profiles and even tubes), and the cast polymer is distinguished by superior mechanical properties and high surface finish... 

The performance of demulsifiers can be predicted by the relationship between the film pressure of the demulsifier and the normalized area and the solvent properties of the demulsifier [1632]. The surfactant activity of the demulsifier is dependent on the bulk phase behavior of the chemical when dispersed in the crude oil emulsions. This behavior can be monitored by determining the demulsifier pressure-area isotherms for adsorption at the crude oil-water interface. 

The determination of the enzyme activity as a function of the composition of the reaction medium is very important in order to find the optimal reaction conditions of an enzyme catalysed synthesis. In case of lipases, the hydrolysis of p-nitrophenyl esters in w/o-microemulsions is often used as a model reaction [19, 20]. The auto-hydrolysis of these esters in w/o-microemulsions is negligible. Because of the microstructure of the reaction media itself and the changing solvent properties of the water within the reverse micelles, the absorbance maximum of the p-nitrophenol varies in the microemulsion from that in bulk water, a fact that has to be considered [82]. Because of this, the water- and surfactant concentrations of the applied micro emulsions have to be well adjusted. 

Princen [57, 64, 82] and others [84] also noted the presence of wall-slip in rheological experiments on HIPEs and foams. However, instead of attempting to eliminate this phenomenon, Princen [64] employed it to examine the flow properties of the boundary layer between the bulk emulsion and the container walls, and demonstrated the existence of a wall-slip yield stress, below that of the bulk emulsion. This was attributed to roughness of the viscometer walls. Princen and Kiss [57], and others [85], have also showed that wall-slip could be eliminated, up to a certain finite stress value, by roughening the walls of the viscometer. Alternatively [82, 86], it was demonstrated that wall-slip can be corrected for and effectively removed from calculations. Thus, viscometers with smooth walls can be used. This is preferable, as the degree of roughness required to completely eradicate wall-slip is difficult to determine. 

The term food colloids can be applied to all edible multi-phase systems such as foams, gels, dispersions and emulsions. Therefore, most manufactured foodstuffs can be classified as food colloids, and some natural ones also (notably milk). One of the key features of such systems is that they require the addition of a combination of surface-active molecules and thickeners for control of their texture and shelf-life. To achieve the requirements of consumers and food technologists, various combinations of proteins and polysaccharides are routinely used. The structures formed by these biopolymers in the bulk aqueous phase and at the surface of droplets and bubbles determine the long-term stability and rheological properties of food colloids. These structures are determined by the nature of the various kinds of biopolymer-biopolymer interactions, as well as by the interactions of the biopolymers with other food ingredients such as low-molecular-weight surfactants (emulsifiers). 

In non-scattering systems, ultrasonic properties and the volume fraction of the disperse phase are related in a simple manner. In practice, many emulsions and suspensions behave like non-scattering systems under certain conditions (e.g. when thermal and visco-inertial scattering are not significant). In these systems, it is simple to use ultrasonic measurements to determine 0 once the ultrasonic properties of the component phases are known. Alternatively, if the ultrasonic properties of the continuous phase, 0and p2 are known, the adiabatic compressibility of the dispersed phase can be determined by measuring the ultrasonic velocity. This is particularly useful for materials where it is difficult to measure jc directly in the bulk form (e.g. powders, granular materials, blood cells). 

This chapter outlines emulsion characterization techniques ranging from those commonly found infield environments to those in use in research laboratories. Techniques used in the determination of bulk emulsion properties, or simply the relative amount of oil, water, and solids present, are discussed, as well as those characterization methods that measure the size distribution of the dispersed phase, rheological behavior, and emulsion stability. A particular emphasis is placed on optical and scanning electron microscopy as methods of emulsion characterization. Most of the common and many of the less frequently used emulsion characterization techniques are outlined, along with their particular advantages and disadvantages. 

After all, the stability and size distribution of this phase determine most bulk emulsion properties. Fixed proportions of oil, water, and solids can be combined in various ways to produce emulsions having different size distributions of the dispersed phase, given only small differences in emulsifier or ion additions to the water or oil phases. These physical differences can lead to significantly different viscosity and stability in emulsions with nominally identical bulk composition. 

The activity of natural antioxidants is greatly affected by complex interfacial phenomena in emulsions and multi-component foods. The methodology to evaluate natural antioxidants must be carefully interpreted depending on whether oxidation is carried out in bulk oils or in emulsions, and which analytical method is used to determine extent and end-point of oxidation (Chapter 10). To understand and better predict how natural antioxidants may protect foods against oxidation, the following complex questions need to be carefully considered for the judicious choice of antioxidant evaluation protocols a) What are the protective properties of antioxidants b) What substrates are oxidized and what products of oxidation are inhibited c) In a multiphase food system is the antioxidant located where oxidation takes place d) Are there any... 

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