Studying emulsion

Squalene is preferred for skin care due to its notably high emollient properties. It can be easily absorbed deep by the skin acting as a normal-izer for flexibility and suppleness of the skin without presenting an oily residue. Blasco et al. (2006) studied emulsions for skin constituents in... 

This aspect of emulsion flotation, however, has not been systematically studied. Emulsion flotation has been employed in the treatment of ores containing, iron, manganese, molybdenum and titanium oxide. (9-11) A major role of emulsion of fatty acids in the flotation of Florida phosphate rock also cannot be... 

For studying emulsion coalescence, it is important to consider the rate constant of flocculation and coalescence. If coalescence is the dominant factor, then the rate K follows a first-order kinetics. 

A more rigorous procedure to study emulsion stability using the ultracentrifuge is to observe the system at various speeds of rotation. At relatively low centrifuge speeds, the expected opaque cream layer may be observed, but at sufficiently high speeds a coalesced oil layer and a cream layer may be observed that are separated by an extra layer of deformed oil droplets. This deformed layer resembles a foam that is, it consists of oil droplets separated by thin aqueous films. 

Figure 2.4-3 (type A) shows an apparatus for studying emulsion formation and stability at pressures up to 345 bar and temperatures up to 80 °C. The emulsion is formed by introducing a liquid into a C02/surfactant solution with a six-port rotary valve (Valeo) and shearing the solution into small droplets by recirculation through a 100 pm i.d. silica capillary with an HPLC pump. The optical cell for DLS contains three windows at right angles and... 

Emulsion droplets cannot only break by coalescing with each other, but they may also break by attaehing to a solid surface. Depending on the application this may be wanted or unwanted. In order to study emulsion-surface interactions a model oil-in-water emulsion was prepared from purified soybean oil (20 wt %) using fractionated egg phosphatides (1.2 wt %) as emulsifier. The major compo-... 

A very important part of emulsion study is the availability of methodologies to study emulsions. In the past ten years, both dielectric methods (1) and rheological methods (2) have been exploited to study formation mechanisms and the stability of emulsions formed from many different types of oils. Standard techniques, including NMR, chemical analysis techniques, microscopy, interfacial pressure, and interfacial tension, are also being applied to emulsions. These techniques have largely confirmed findings noted in the dielectric and rheological mechanisms. 

Twardus studied emulsions in 1980 and found that emulsion formation might be correlated with oil composition (6). It was suggested that asphaltenes and metal porphyrins contributed to emulsion stability. Bridie et al. (7) studied emulsions in the same year and proposed that the asphaltenes and waxes stabilized water-in-oil emulsions. The wax and asphaltene content of two test oils correlated wifli the formation of emulsions in a laboratory test (7). Mackay and Zagorski hypothesized that emulsion stability was due to the formation of a film in oil that resisted water-droplet coalescence (8—10). The nature ofthese thin films was not described, but it was proposed that they were caused by the accumulation of certain types of compounds, later work led to the conclusion that the eompounds were asphaltenes and waxes. A standard procedure was devised by making emulsions and measuring stabihty. This work formed the basis of much of the emulsion flieory and emulsion formation in the oil-spill literature over the past two decades. 

In 1983, Thingstad and Pengeurd conducted photo-oxidation experiments and found that photo-oxidized oil formed emulsions (11). Nesterova et al. studied emulsion formation and concluded that it was strongly correlated with both the asphaltene and tar content of oil and also the salinity of the water with whieh it was formed (12). Mackay and Nowak studied emulsions and found that stable emulsions had low conductivity and therefore a continuous phase of oil (13,14). Stability was discussed and proposed to be a funetion of oil composition, particularly waxes as asphaltenes. It was proposed that a water droplet could be stabilized by waxes, asphaltenes, or a combination of both. The viscosity of the resulting emulsions was correlated with water content. Later work by the same group reported examination of Russian hypotheses that emulsions are stabilized by colloidal particles which gather at the oil— water interface and may combine to form a near-solid barrier that resists deformation and thus water-water coalescence (15). It was speculated that these particles could be mineral, wax crystals, aggregates of tar and asphaltenes, or mixtures of... 

In the oil-spill trade, much of the information on emulsions has been obtained by practical studies in the laboratory or the field. In 1991, Jenkins et al. studied emulsions formed in the laboratory and concluded that the formation did not correlate with previously established codes of properties, nor with pour point, asphaltene, and wax contents of the fresh oils (19). Jenkins et al. suggested that, in the absence of any correlation, characterization of every oil should be... 

SjOblom et al. used dielectric spectroscopy to study emulsions over a period of years (42). It is concluded that the stabilizing fraction in water-in-oil emulsions is the asphaltenes and not the resins. However, it is noted that some resins must be present to give rise to stability. It is suggested that the greater mobility of the resins is needed to stabilize the emulsions until the asphaltenes, which migrate slowly, can align at the interface and stabilize the emulsions. 

One of the methods used to study emulsions has been the use of dielectric spectroscopy. The permittivity of the emulsion can be used to characterize an emulsion and assign a stability (1,42,48—54). The Sjoblom group has measured the dielectric spectra using time-domain spectroscopy (TDS) technique. A sample is placed at the end of a coaxial line to measure total reflection. Reflected pulses are observed in time windows of 20 ns, Fourier transformed in the frequency range from 50 MHz to 2 GHz, and the complex permittivity calculated. Water or air can be used as reference sample. The total complex permittivity at a frequency (co) is given by ... 

The crudes span geographically over large areas North Sea, European continent, Afiica, Asia, etc. This is a necessity since if the crude oils in the test matrix are interrelated one cannot universalize the results. Table 1 lists the erude oils and their origin. To start with we determined the inversion point (or alternatively, the maximum eontent of water that can be introduced into the oil without a phase separation). We have ehosen to study emulsions that are 10% below the inversion point Exeeptions in this respeet are the two European erodes with 5% water stabilized. The erode oils were eharacterized by means of density, surfaee tension, and viseosity measurements. The results are summarized in Table 2. All experiments involving emulsions were carried out at 50°C. The reason for working at elevated temperature is to melt the wax in the oils and thereby prevent the influence of the wax on emulsion stability. The elevated temperature is also more elosely related to the real working temperature used in the proeesses in the field. 

A brief introduction explaining the motivation and rationale to study emulsion systems using spectroscopic techniques is presented in this section. 

Silva et al. used low-field CPMG experiments, providing T2 distributions, for quantitative analysis of mixtures involving crude oils and water. Kashaev and Fashkiev reported relaxation studies of concentrated oil-in-water emulsions. Melnikov and co-workers studied emulsions of water in poly(ethylsiloxane) fluid, prepared by mechanical dispersion, in the presence of freon gas. At low temperatures and under pressure of freon, the... 

Table 1 summarizes the values of rheological parameters of some studied emulsion films stabilized by the gelatin/ lecithin complexes. These parameters were measured immediately after the film formation (at 1 min). It is worth noting that the yield stress, elastic modules and film shear viscosity increase in the increase of the lecithin concentration. Analysis of the experimental data demonstrates that the parameters of the films (when films have been formed during several minutes) have values in the same order as the analogous characteristics of the layer formed after 4 hours. 

In the early 1950s, Barkas and coworkers studied emulsion tracks of positive and negative pions. 

It has not been yet mentioned that the dispersed solid droplets melt at the same temperature. The determinations of thermal signal shape and area are similar to those for bulk systems if the continuous medium does not show high thermal resistance. To reach those conditions, the heating rate has to be less than 2 K/ min and the mass sample sufficiently small. To study emulsions quantitatively, it is necessary to know precisely the total mass of dispersed liquid, trii. The... 

This section is not intended to be a rheology course, but it will tell how to use rheology as a very powerful tool for studying emulsions. Nevertheless, a quick recap of the rheology fundamentals is very helpful. 

Shinoda also studied emulsions that were produced at temperatures below the PIT, at the PIT and above the PIT with rapid cooling to aid stability. Drop sizes of emulsions produced at the PIT were retained in the final cooled emulsion. Shinoda noted that emulsions with the finest drops were produced by emulsifying 2-4 C below the PIT and then cooling. Shinoda termed this emulsification method emulsification by the PIT method . The study also showed that emulsification by the inversion method , i.e. emulsification above the PIT as a W/O emulsion and then cooling, did not result in such small drops. 

Kato et al. [310] studied emulsion polymerization of styrene in the presence of sodium dodecyl sulfate and lithium perfluorooctanesulfonate. The fluorinated surfactant decreases the polymerization rate and the molecular weight of the polymer formed. 

When studying emulsion stability, it may be helpful to realize that in a pure oil and pure water mixture, without an emulsifying agent, no amount of agitation will create an emulsion. If the pure oil and water are mixed and placed in a container, they quickly separate. The natural state is for the immiscible liquids to establish the least contact or smallest surface area. The water dispersed in the oil forms spherical drops. Smaller drops will coalesce into larger drops, and this will create a smaller interface area for a given volume. If no emulsifier is present, the droplets will eventually settle to the bottom, causing the smallest interface area. This type of mixture is a true "dispersion."... 

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