Emulsion conductivity measurements

M Bury, J Gerhards, W Erni, A Stamm. Application of a new method based on conductivity measurements to determine the creaming stability of O/W emulsions. Int Pharm 124(2) 183 194, 1995. 

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

Reimers and Schork [94, 95] report the use of PMMA to stabihze MM A miniemulsions enough to effect predominant droplet nucleation. Emulsions stabilized against diffusional degradation by incorporating a polymeric costabilizer were produced and polymerized. The presence of large numbers of small droplets shifted the nucleation mechanism from micellar or homogeneous nucleation, to droplet nucleation. Droplet diameters were in the miniemulsion range and reasonably narrowly distributed. On-hne conductance measurements were used to confirm predominant droplet nucleation. The observed reaction rates were dependent on the amount of polymeric costabilizer present. The latexes prepared with polymeric costabilizer had lower polydispersities (1.006) than either latexes prepared from macroemulsions (1.049) or from alkane-stabilized miniemulsions (1.037). 

The results of tests conducted using the pressure-atomizing nozzle with emulsified fuels are presented in Figures 11 and 12. They are expressed in terms of the effect of increased water addition on combustion eflBciency and pollutant emission rates. The data in Figure 11 indicate that combustion eflBciency increased with increased water addition, reaching a maximum at approximately 5% water added, and thereafter decreased, perhaps as a result of local quenching in the primary zone caused by water addition. A 15% increase in eflBciency relative to that attained with neat fuel was obtained using a 5% emulsion. The measured eflBciency for operation with No. 2 fuel oil is shown for comparison, and differences... 

The concentric cylinder viscometers are supplied with different inner and outer cylinders such that various gap widths can be formed. For rheological measurements of emulsions and suspensions, care must be taken to ensure a gap width of at least 20 times the suspended particle size in order to avoid wall effects. Moreover, experiments should be conducted with different gap widths to ensure the absence of any wall slip that is usually encountered in emulsion viscosity measurements (J6). However, uniformity of shear rate can be achieved only when the ratio of the gap width to the inner cylinder radius is small. 

In general, an emulsion exhibits the characteristics of its external phase. Several methods are available for identifying the emulsion type. Dilution tests are based on the fact that the emulsion is only miscible with the liquid that forms its continuous phase. Conductivity measurements rely on the poor conductivity of oil compared with water, and give low values in w/o emulsions where oil is the continuous phase. Staining tests in which a water-soluble dye is sprinkled onto the surface of the emulsion also indicate the nature of the continuous phase. With an o/w emulsion there is rapid incorporation of the dye into the system whereas with the w/o emulsion the dye forms microscopically visible clumps. The reverse happens on addition of an oil-soluble dye. These tests essentially identify the continuous phase and do not indicate whether a multiple emulsion has been produced. This can be resolved by microscopy. 

Earlier conductivity measurements have indicated that the most stable miniemulsions are produced with mixed emulsifier molar ratios between 1 1 and 1 3 (22,23). This correlation agrees with a theoretical analysis of mixed emulsifier adsorption onto oil droplets by Lucassen-Reynders (35), who have determined the optimum stability to occur at molar ratios near 1 1. However, the maximum interfacial tensions at these molar ratios were unexpected because, minimum interfacial tensions are usually associated with maximum emulsion stability. In fact, minima values substantially less than 1 dyne/cm have been reported for several oil/mixed emulsifier systems (31,33, 36,37). 

Water-C02 Emulsions and C02-Water Emulsions Conductivity and Dielectric Measurements... 

Scattering techniques provide the most definite proof of micellar aggregation. Zielinski et aL (34) employed SANS to study the droplet structures in these systems. Conductivity measurements (35) and SANS (36) were also used to study droplet interactions at high volume fraction in w/c microemulsions formed with a PFPE-COO NH4 surfactant (MW = 672). Scattering data were successfully fitted by Schultz distribution of polydisperse spheres (see footnote 37). A range of PFPE-COO NH/ surfactants were also shown to form w/c emulsions consisting of equal amount of CO2 and brine (38-40). 

Figure 7.11. Light-responsive and reversible inversion of emulsion (dodecane/ water+NaNOs). The conductivity measurements indicate the type of continuous phase (conducting water vs. insulating oil) in samples maintained under gentle agitation (stirring bar). The emulsifier contains an azobenzene-modified polyacrylate (n = 5, x=3% in Fig. 7.1) and a temperature-responsive surfactant (C12E4) that in absence of polymer would stabilize inverse emulsion above 24°C. (a) Temperature sweep of the same sample exposed to UV or blue light, (b) Switches of the wavelength of exposure between UV and blue lights at fixed temperature (25°C) at times pointed by arrows.

The emulsion stability map is constnicled in a similar way. Emulsions made from preequilibrated systems according to the standard procedure are left to settle and their stability is measured as the time for some settling, e.g., 50%, to take place. Sufficient measurements should be carried out so that isostability contours might be drawn. As with conductivity measurements a clever location of tested systems according to the expected pattern could greatly improve the experimental yield. 

II. CONDUCTIVITY MEASUREMENTS AND INFLUENCE OF KRAFT LIGNIN AND LIGNOSULFONATE CONCENTRATION ON EMULSION STABILITY... 

Table SSeparation of Water from OAV Emulsions Stabilized with Lignosulfonate (UP364) and Lignosulfonate/CPC Complexes Calculated from Conductivity Measurements and Visual Observations...

The conductivity measurements were performed using the same instrumentation as described in Sec. II.A.2. Figure 8 shows how the electrodes were placed in the sample cell containing the emulsion. The two electrode pairs were designed to measure the conductivity in the lower and the upper part of the emulsion, respectively. This was achieved by insulating parts of the electrodes with Teflon tubes. By using this design the conductivity was measured in the lower 35 mm and the upper 35 mm of the sample container. 

Figure 9 Reproducibility of the conductivity measurements of lignosulfonate-stabilized emulsions measured at 25°C.

The effect of the Tg of the latex on the film-formation behaviour of a series of 2-ethylhexyl acrylate/methyl methacrylate emulsion copolymers was studied. Stage 1 of fihn formation was examined using a combination of DMA and conductivity measurements. Stages 2 and 3 were investigated using calorimehic compensation, DSC, dielectric spectroscopy and atomic force microscopy. Comparison of the results from the different methods employed led to a detailed model of the film-formation process in which the temp, used relative to the minimum film-formation temp, determined the effectiveness of the processes. The relative usefulness of the techniques used in their ability to characterise the various stages in the film-formation process was assessed for these copolymer systans. 23 refs. 

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. 

Other qualitative applications of this type include a study of the differentiation between the intervals of emulsion polymerization [34] and mechanisms of nucleation [35, 36], the swelling of emulsion polymers [37], the partitioning of surfactants [38], and the monitoring of the state of emulsion polymerizations [39]. It has also been demonstrated that particle coagulation could be detected by conductivity measurements [40]. 

Santos AF, Pinto JC, McKenna TFL.On-Une monitoring of the evolution of number of particles in emulsion polymerization by conductivity measurements. Part I. Model formulation. J Appl Polym Sci 2003 90 1213-1226. 

Graillat C, Santos AF, Pinto JC, McKenna TFL. On-line monitoring of emulsion polymerisation using conductivity measurements. Macromol Symp 2004 206 433-442. 

Dahms and Ludwig [13] discussed the two methods. Refer also to the low-energy emulsification process discussed in Sec. VI. The same method was used by Marszall [14] to determine the required HUB of the emulsifier. He used the emulsion-inversion point concept (EIP). The EIP is determined with conductivity measurements by adding increments (1 cm ) of water to a measiured amotmt (50 cm ) of oil in which the emulsifiers are dissolved (Fig. 12). He found that the required HLB corresponds to the minimum EIP. 

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. 

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