Viscosity emulsions

Latex Types. Latexes are differentiated both by the nature of the coUoidal system and by the type of polymer present. Nearly aU of the coUoidal systems are similar to those used in the manufacture of dry types. That is, they are anionic and contain either a sodium or potassium salt of a rosin acid or derivative. In addition, they may also contain a strong acid soap to provide additional stabUity. Those having polymer soUds around 60% contain a very finely tuned soap system to avoid excessive emulsion viscosity during polymeri2ation (162—164). Du Pont also offers a carboxylated nonionic latex stabili2ed with poly(vinyl alcohol). This latex type is especiaUy resistant to flocculation by electrolytes, heat, and mechanical shear, surviving conditions which would easUy flocculate ionic latexes. The differences between anionic and nonionic latexes are outlined in Table 11. 

The nomograph (Figure 3) finds the emulsion viscosity of nonmiscible liquids and is based on the following equation ... 

Example. The viscosity of the continuous phase liquid is 20. The viscosity of the dispersed phase liquid is 30. The volume fraction of the dispersed phase liquid is 0.3. The nomograph shows the emulsion viscosity to be 36.2. 

Zanker, Adam, Find Emulsion Viscosity Through Use of Nomograph, Hydrocarbon Processing, January 1969, p. 178. 

Emulsion blocks within the formation can form as a result of various well treatments and are more easily prevented (by using surfactants in conjunction with well treatments, see above) than removed. Aromatic solvents can be used to reduce the viscosity and mobilize oil-external emulsions (167). Low molecular weight urea-formaldehyde resins have been claimed to function in a similar manner in steam and water injection wells (168,169). Water-external emulsion blocks can be mobilized by injection of water to reduce emulsion viscosity. 

The model system used by Mabille et al. [149, 150] was a set of monodisperse dilute (2.5 wt% of dispersed oil) emulsions of identical composition, whose mean size ranged from 4 p.m to 11 p.m. A sudden shear of 500 s was applied by means of a strain-controlled rheometer for durations ranging from 1 to 1500 s. All the resulting emulsions were also monodisperse. At such low oil droplet fraction, the emulsion viscosity was mainly determined by that of the continuous phase (it was checked that the droplet size had no effect on the emulsion viscosity). The viscosity ratio p = t]a/t]c = 0.4 and the interfacial tension yi t = 6 mN/m remained constant. 

This work shows that high shear rates are required before viscous effects make a significant contribution to the shear stress at low rates of shear the effects are minimal. However, Princen claims that, experimentally, this does not apply. Shear stress was observed to increase at moderate rates of shear [64]. This difference was attributed to the use of the dubious model of all continuous phase liquid being present in the thin films between the cells, with Plateau borders of no, or negligible, liquid content [65]. The opposite is more realistic i.e. most of the liquid continuous phase is confined to the Plateau borders. Princen used this model to determine the viscous contribution to the overall foam or emulsion viscosity, for extensional strain up to the elastic limit. The results indicate that significant contributions to the effective viscosity were observed at moderate strain, and that the foam viscosity could be several orders of magnitude higher than the continuous phase viscosity. 

Data in Table I show that emulsion capacity of peanut flour decreased with increasing flour or protein concentration while emulsion viscosity increased. This phenomenon was also demonstrated by McWatters and Holmes (2D. A decrease in flour particle size increased emulsion capacity and viscosity appreciably. Increasing the rate of mixing, however, decreased emulsion capacity but increased viscosity. Increased speeds produce greater shear rate, which decreases the size of the oil droplet thus, there is an increase in the surface area of the oil to be emulsified by the same amount of soluble protein (23, 24). 

There are a number of key points to be made about the variables used In the equations. First, the equation forms used for the high salt concentration (1.0 M NaCl) are simple quadratic and cubic forms using pH and the square and cube of pH as Independent variables. The high salt concentration negated the emulsion Inhibiting effects of the Isoelectric point. The percent of the variation In the function properties accounted for by these equations ranged from about 80 percent for emulsion viscosity to over 98 percent for emulsion capacity. 

Although they are a relatively small volume product—approximately 75,000 tons produced in 1949 (126)—interest in asphalt emulsion has continued at a high level. Abraham (6) has reviewed the patent literature relative to the types of emulsifying agents used, while commercial practice has been discussed by Day (16). The most common emulsifiers are sodium or potassium soaps of tall oil, abietic acid, or Vinsol resin, or colloidal clays such as bentonite for adhesive base emulsions. Lyttleton and Traxler (53) studied the flow properties of asphalt emulsions, and Traxler (122) has investigated the effect of size distribution of the dispersed particles on emulsion viscosity. A decrease in particle size uniformity was found to be accompanied by a decrease in consistency because particles of various size assume a more loosely packed condition than do those of the same size. 

If the quantity of oil to be fixed in a dried powder is a parameter dependent on the end use, the formulator can choose between different Acacia gums. With a traditional Acacia gum (exudate of Acacia Senegal), a dry substance value of 35% represents a maximum value before spray drying. Beyond this value the emulsion viscosity is too high and drying inside the atomization tower does not take place satisfactorily. 

Measurement of the emulsion viscosities at different temperatures, shear rates and water cuts. 

Emulsion viscosities have been measured as a function of water content (10, 20 and 40S), temperature and shear rate in a thermostatted rotating viscometer. The shear rates were varied between 0.277 and 27.7 s"1 with measurements taken at temperatures between 5 and 20° C. Above 20°C, separation of water from the emulsion occurred, rendering viscosity measurements unreliable. The apparent viscosity of the emulsion below 20° C increases drastically with the watercut in the emulsion and decreases with Increasing shear rate (Fig. 5). Emulsions containing more than 20X water were found to behave as pseudo-plastic fluids. 

Example. Bitumen is recovered in the form of a froth when a separation-flotation process is applied to surface mined oil sand. Once de aerated, this bituminous froth is a W/O emulsion from which the water must be removed prior to upgrading and refining. At process temperature (80 °C) the emulsion viscosity is similar to that of the bitumen, but the density, due to entrained solids, is higher. Taking t) = 500 mPa-s and f> = 1.04 g/mL, the rate of creaming of 20 pm diameter water droplets under gravitational force will be very slow ... 

The texture of an emulsion frequently reflects that of the external phase. Thus O/W emulsions usually feel watery or creamy while W/O emulsions feel oily or greasy . This distinction becomes less evident as the emulsion viscosity increases, so that a very viscous O/W emulsion may feel oily. 

In addition to influencing stability, the nature of the emulsifier can also have an influence on droplet size distribution, the mean droplet size, and also on emulsion viscosity [215] (see also Section 6.5.5). 

For electrostatically or sterically interacting drops, emulsion viscosity will be higher when droplets are smaller. The viscosity will also be higher when the droplet sizes are relatively homogeneous, that is, when the drop size distribution is narrow rather than wide. The nature of the emulsifier can influence not just emulsion stability but also the size distribution, mean droplet size, and therefore the viscosity. To describe the effect of emulsifiers on emulsion viscosity Sherman [215] has suggested a modification of the Richardson Equation to the following form ... 

If the internal phase in an emulsion has a sufficiently high volume fraction (typically anywhere from 10 to 50%) the emulsion viscosity increases due to droplet crowding, or structural viscosity, and becomes non-Newtonian. The maximum volume fraction possible for an internal phase made up of uniform, incompressible spheres is 74%, although emulsions with an internal volume fraction of 99% have... 

Since wet foams contain approximately spherical bubbles, their viscosities can be estimated by the same means that are used to predict emulsion viscosities. In this case the foam viscosity is described in terms of the viscosity of the continuous liquid phase (tjo) and the amount of dispersed gas (4>). In dry foams, where the internal phase has a high volume fraction the foam viscosity increases strongly due to bubble crowding, or structural viscosity, becomes non-Newtonian, and frequently exhibits a yield stress. As is the case for emulsions, the maximum volume fraction possible for an internal phase made up of uniform, incompressible spheres is 74%, but since the gas bubbles are very deformable and compressible, foams with an internal vol-... 

Several practical formulae have been developed for estimating the effect on emulsion viscosity of changes in key variables such as temperature, water content, and droplet size distribution, in which adjusting factors for each property are obtained from empirical correlations. An illustration is provided by Rimmer et al. [763]. Such formulae may also contain a term representing changes in emulsion droplet size due to droplet coalescence that occurs with time as the emulsion moves through the pipeline ( ageing ). 

Type and concentration of emulsifier. The viscosity and yield value of emulsions (chemical nature of the emulsifier. Sherman (1955c) proposed two possible reasons for this, namely interfacial viscosity and interfacial adsorption. Interfacial viscosity affects the resistance of droplets to deformation, which is reflected in the resulting emulsion viscosity. A high level of interfacial adsorption enlarges the size of the interfacial layer significantly and increases emulsion viscosity. Adsorption of emulsifier at the interface should also increase with the concentration of emulsifier. The... 

As already outlined, the higher the viscosity of the continuous oil phase, the higher the viscosity of the emulsion. At high emulsion viscosity, the stability to coalescence is increased, and may result in increased stability... 

Sherman, P. 1950. Studies in water-in-oil emulsions. I. The influence of disperse phase on emulsion viscosity. J. Soc. Chem. Ind., Suppl. Issue No. 2, S70-S74. 

The previous experiments were all performed on dilute emulsions for which the dispersed phase represents 2.5 wt % of the emulsion. As 0 increases, the relative contribution of the fast regime becomes more pronounced. As could be expected, the more concentrated the emulsion, the smaller the final size this tendency merely reflects the fact that the emulsion viscosity and... 

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