Electrical conductivity emulsions, measurement

A wellbore fluid has been developed that has a nonaqueous continuous liquid phase that exhibits an electrical conductivity increased by a factor of 10 to 10 compared with conventional invert emulsion. 0.2% to 10% by volume of carbon black particles and emulsifying surfactants are used as additives. Information from electrical logging tools, including measurement while drilling and logging while drilling, can be obtained [1563]. 

One way is to measure the electrical conductivity. An oil-in-water emulsion has a higher conductivity because water as the continuous phase has a much higher conductivity than oil. 

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. 

A fourth way is to count droplets individually. First, one has to dilute the emulsion strongly. Then, this diluted emulsion is pushed through a small hole. At the same time, the electrical conductivity through the hole is measured. Every time an emulsion droplet moves through the hole, the droplet will obscure part of the hole, which suddenly reduces the conductivity through the hole— the larger the droplet is, the stronger is the effect. Also in this way a droplet size distribution can be obtained. This method is usually referred to as the Coulter counter method, after an important manufacturer of this type of equipment. 

The stability of the water-in-oil emulsion is quite important in low-fat spreads, and electrical conductivity gives a measure of this. Electrical conductivity can be followed during production through suitably designed measuring cells mounted in the process line or be measured directly on product samples in tubs (91). 

Different methods [120] such as volume variation, internal phase droplet size variation, viscosity variation, density variation, tracer method, Karl-Fischer method, and electrical conductivity have been employed in the measurement of emulsion swelling. The data obtained tends to be as varied as the methods used [120]. One major drawback is that none of the above methods is capable of determining both emulsion swelling and membrane breakage in the same experiment. Further, osmotic swelling cannot be differentiated from entrainment swelling. 

Polymerisable monoquatemary, and structurally related diquatemary anunonium bromide cationic surfactants were synthesised, together with non-polymerisable analogues of each type of surfactant. The surface activity properties of all the surfactants were studied by means of surface tension and electrical conductivity measurements and the results were discussed with reference to the molecular structure of the surfactants and the valency of the salts. Each surfactant was used as the emulsifier for emulsion polymerisation of styrene and of methyl methacrylate and in each case, well defined stable polymer latexes were formed. The results of stability investigations were discussed with reference to the molecular structure of the surfactants. Comparisons were made between the effectiveness of polymerisable and non -polymerisable surfactants and between dicationic and monocationic species. 49 refs. 

The electrical conductivity of a fluid is a quantitative measure of its ability to carry an electrical current, and therefore depends to a large extent on the concentration of ionic species. Given that the conductivity of pure water is extremely low (limited to 0.0548 xScm" at 25 °C by the HjO dissociation constant into H and OH" when no added ions are present), this technique will be sensitive to changes in ionic concentration. So, while it is not impossible to be used for the online monitoring of solution or melt phase processes, it is better suited for use in emulsion and miniemulsion polymerization reactions where ionic surfactants and initiators are commonly employed. 

Measurements of the bulk solution properties (e.g., surface tension, electrical conductivity, fluorescence, and light scattering intensity) as a function of surfactant concentration can be used to determine the CMC. As shown schematically in Figure 2.2, the point at which the sudden change in surface tension occurs is taken as the CMC of the aqueous surfactant solutions. How to establish the correlation between the CMC data and the molecular structure of surfactants is of great importance in the selection of optimum surfactants for the effective stabilization of various emulsion polymerization systems. This subject will be the focus of the following discussion. 

A phase inversion plot was developed for the Cjg alkyldiphenyl oxide disul-fonate/alcohol ethoxylate blends at a temperature of 35°C (Fig. 5). The y-inter-cept in this plot is equivalent to the optimal composition of the surfactant film. This composition provides the lowest oil-water interfacial tension at a given temperature. If the ratio of nonionic surfactant to anionic surfactant is lower than the optimum, the system is too hydrophilic in nature and tends to form an oil-inwater emulsion. Similarly, if the ratio of nonionic surfactant to anionic surfactant is higher than the optimum, a water-in-oil emulsion forms. The plot shown in Figure 5 was developed by using electrical conductivity measurements as outlined by Raney [12] to identify the transition from a high-conductivity oil-in-water emulsion to a low-conductivity water-in-oil emulsion. 

To determine the optimum loading of graphene for preparation porous conductive scaffolds, electrical conductivity of synthesized PANI (emulsion and solution polymerization samples) containing various amount of graphene was measured. After determining the percolation threshold of... 

FIGURE 1.18 Electrical conductivity of PANI/graphene nanocomposites (a) solution polymerization, and (b) emulsion polymerization method (each data is the average of 3 times measuring). 

The factor (1 in Eq. (2) measures the tangential electric field at the particle siuface. It is this component which generates the electrophoretic or electroacoustic motion. For a fixed frequency, it can be seen from Eq. (4) that (1 +J) depends on the permittivity of the particles and on die function X - Kg/K a, where Ks is the surface conductance of the double layer X measures the enhanced conductivity due to the charge at the particle surface. It is usually small unless the zeta potential is very high, so for most emulsions with large ka, X has a negligible effect. The ratio fp/f is also small for oil-in-water emulsions. Equation (4) can then be reduced to/= 0.5 and hence the dynamic mobility becomes ... 

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