Conductivity of emulsions

Of the numerous equations proposed [37] to describe the conductivity of emulsions (kf), two are cited here for illustration. If the conductivity of the dispersed phase (kd) is much less than that of the continuous phase (kc), kc kd,... 

Measurement of the electrical conductivity of emulsions has been considered as an alternative method since oil-in-water emulsions exhibit higher conductivity than water-in-oil emulsions (Rshl, 1972). However, this method which has been used with some success to control the level of water in butter (Prentice, 1953), has the disadvantage of being dependent on ion concentration. Therefore, certain added ions increase conductivity but might not increase stability to inversion. 

Consider now the case of motion of emulsion drops in an electric field (this case is important for many applications). In contrast to the case considered above, electric conductivity of emulsion drops can be smaller or equal to that of the external liquid. For such a system, an electric field can exist inside the drop, and the condition (9.41) holds not only for the external, but also for the internal liquid. 

Figure 1.1 Conductivity of emulsions (

An emulsion may be defined as a mixture of particles of one liquid with some second liquid. The two common types of emulsions are oil-in-water (O/W) and water-in-oil (W/0), where the term oil is used to denote the water-insoluble fiuid. These two types are illustrated in Fig. XIV-1, where it is clear that the majority or outer phase is continuous, whereas the minority or inner phase is not. These two emulsion types are distinguished by their ability to disperse oil or water-soluble dyes, their dilution with oil or water, and their conductivity (O/W emulsions have much higher conductivity than do W/0 ones see Ref. 1 for reviews). 

The conductivity of a dilute emulsion can be treated by classic theory (see Maxwell [6]) assuming spherical droplets... 

Suppose that the specific conductivities of an oil and a liquid phase are 2 x 10 and 2 x 10 0 cm , respectively. Calculate and plot versus the specific conductivities of O/W and W/0 emulsions formed from these phases. 

Hollow and porous polymer capsules of micrometer size have been fabricated by using emulsion polymerization or through interfacial polymerization strategies [79,83-84, 88-90], Micron-size, hollow cross-linked polymer capsules were prepared by suspension polymerization of emulsion droplets with polystyrene dissolved in an aqueous solution of poly(vinyl alcohol) [88], while latex capsules with a multihollow structure were processed by seeded emulsion polymerization [89], Ceramic hollow capsules have also been prepared by emulsion/phase-separation procedures [14,91-96] For example, hollow silica capsules with diameters of 1-100 micrometers were obtained by interfacial reactions conducted in oil/water emulsions [91],... 

Meredith, RE Tobias, CW, Conductivities in Emulsions, Journal of the Electrochemical Society 108, 286, 1961. 

Polymerizations conducted in nonaqueous media in which the polymer is insoluble also display the characteristics of emulsion polymerization. When either vinyl acetate or methyl methacrylate is polymerized in a poor solvent for the polymer, for example, the rate accelerates as the polymerization progresses. This acceleration, which has been called the gel effect,probably is associated with the precipitation of minute droplets of polymer highly swollen with monomer. These droplets may provide polymerization loci in which a single chain radical may be isolated from all others. A similar heterophase polymerization is observed even in the polymerization of the pure monomer in those cases in which the polymer is insoluble in its own monomer. Vinyl chloride, vinylidene chloride, acrylonitrile, and methacryloni-trile polymerize with precipitation of the polymer in a finely divided dispersion as rapidly as it is formed. The reaction rate increases as these polymer particles are generated. In the case of vinyl chloride ... 

The dielectric constant can be used as a criterion for screening, ranking, and selecting demulsifiers for emulsion breaking. In a study, the dielectric constants of emulsions and demulsifiers were measured using a portable capacitance meter, and bottle tests were conducted according to the API specification [18]. The results showed that the dielectric constants can be used effectively to screen and rank demulsifiers, whereas a confirmatory bottle test should be conducted... 

From the experiments it is clear that poly electrolyte is adsorbed on the surface of the black lipid film. This applies both to the experiments with gelatin and bovine serum albumin, which gave no decrease of film resistance, and to the experiments with bovine erythrocyte ghost protein and polyphosphate. The adsorption of protein on the phospholipid-water interface may be controlled independently by investigating the electrophoretic behavior of emulsion droplets, stabilized by phospholipid, in a protein solution, as a function of pH. In this way Haydon (3) established protein adsorption on the phospholipid-water interface. If the high resistance (107 ohms per sq. cm.) of black lipid films is to be ascribed to the continuous layer of hydrocarbon chains in the interior of the film, as is generally done, an increase in film conductivity is not expected from adsorption without penetration. 

POLAR. Descriptive of a molecule in which the positive and negative electrical charges are permanently separated, as opposed to non-polar molecules in which the charges coincide, Polar molecules ionize in solution and impart electrical conductivity. Water, alcohol, and sulfuric acid are polar in nature most hydrocarbon liquids are not. Carboxyl and hydroxyl groups often exhibit an electric charge, The formation of emulsions and the action of detergents are dependent on tills behavior,... 

Latreille, B. and Paquin, P. 1990. Evaluation of emulsion stability by centrifugation with conductivity measurements. J. Food Sci. 55 1666-1672. 

They reasoned that in the vicinity of a silver sulfide speck the conduction band is bent downward and photoelectrons could reach the surface of the crystal more easily, and hence more readily form surface image. However, the thickness of the silver sulfide layer in their experiments was about 4 pm, which far exceeds that of any sensitivity center on emulsion grains. The relevance of their observation to S-sensitization of emulsions is doubtful. Starbov (147) found no evidence of change in the surface potential when either the (111) or the (200) surface of an evaporated silver bromide layer was sulfur-sensitized. 

The electrical conductivity of dilute emulsions can be treated by classical electrodynamic theory and the conductivity is given by... 

In the emulsion phase/packet model, it is perceived that the resistance to heat transfer lies in a relatively thick emulsion layer adjacent to the heating surface. This approach employs an analogy between a fluidized bed and a liquid medium, which considers the emulsion phase/packets to be the continuous phase. Differences in the various emulsion phase models primarily depend on the way the packet is defined. The presence of the maxima in the h-U curve is attributed to the simultaneous effect of an increase in the frequency of packet replacement and an increase in the fraction of time for which the heat transfer surface is covered by bubbles/voids. This unsteady-state model reaches its limit when the particle thermal time constant is smaller than the particle contact time determined by the replacement rate for small particles. In this case, the heat transfer process can be approximated by a steady-state process. Mickley and Fairbanks (1955) treated the packet as a continuum phase and first recognized the significant role of particle heat transfer since the volumetric heat capacity of the particle is 1,000-fold that of the gas at atmospheric conditions. The transient heat conduction equations are solved for a packet of emulsion swept up to the wall by bubble-induced circulation. The model of Mickley and Fairbanks (1955) is introduced in the following discussion. 

Consider a packet of emulsion phase being swept into contact with the heating surface for a certain period. During the contact, the heat is transferred by unsteady-state conduction at the surface until the packet is replaced by a fresh packet as a result of bed circulation, as shown in Fig. 12.6. The heat transfer rate depends on the rate of heating of the packets (or emulsion phase) and on the frequency of their replacement at the surface. To simplify the model, the packet of particles and interstitial gas can be regarded as having the uniform thermal properties of the quiescent bed. The simplest case is represented by the problem of one-dimensional unsteady thermal conduction in a semiinfinite medium. Thus, the governing equation with the boundary conditions and initial condition can be imposed as... 

---