Emulsion viscosity factors affecting

The influence of phase volume on the flow properties of an emulsion is shown in Fig. 7.26. In this diagram the relative viscosity of the system increases with increasing 4>, and at any given phase volume increases with decreasing mean particle size, D. These and other factors which affect emulsion viscosity are listed in Table 7.6. 

The thickening mechanisms of linear carboxyl-containing emulsion polymers have been studied in considerable detail. The polymer molecules of AST emulsions are initially in a coiled configuration within individual latex particles of submicrometer size, and the viscosity of the diluted latex emulsion is similar to that of water prior to neutralization. On the addition of base, the carboxyl groups are ionized, and hydrophilic polymer is formed within the particles. Depending on various factors, which will be elaborated on later in this chapter under the section entitled Factors Affecting the Swelling Dissolution Behavior of Conventional ASTs , the particles may only swell or dissolve completely, or the surface polymer may dissolve and leave swollen cores. 

The interfaeial shear viscosity is measured with an SVR I S Interfaeial Viscoelastic Meter (Kyowa Kagaku Co. Ltd, Japan). The schematic of flie measuring part of the interfacial viscoelastic meter is shown in Fig. 1. The results show that the higher the interfaeial shear viscosity of the interfacial film between jet fuel and water the more stable are the emulsions stabilized by the asphaltene or resin fractions from crude oils (18). We also found that flie value of the interfacial shear viscosity is affected by the following factors (see below). 

A number of factors affect the rheology of emulsions composition, the viscosity ratio of the dispersed-to-matrix phase (1 s 7/2/771), the droplet size and its distribution, rheology of the interphase, and so on. Often, well-stabilized emulsions follow the viscosity-concentration relationships developed for hard sphere suspensions, including the yield phenomena. In contrast, emulsions with deformable dispersed... 

The main factors which affect the viscosity of emulsions are listed in Table 8.6. The properties of the disperse phase, the continuous phase and the emulsifying agent or agents all influence the emulsion viscosity. Each factor does not act independently and the interpretation of emulsion viscosity data is complicated by this fact and the fact that particles can deform under shear depending on the nature of the interfacial film. As we have also discussed, emulsions are complex systems, often highly structured, and at phase boundaries or on the point of inversion are very sensitive to small perturbations in the system. We will deal here first with mobile emulsions and then consider briefly the semi-solid state. 

The third mechanism by which proteins affect the stability of emulsions is rheological. This mechanism derives fundamentally from electrostatic and steric effects. The importance of viscosity has been described earlier. The viscosity of a caseinate solution is, inter alia, an indicator of the degree of bound water absorbed by the hydrophilic groups, as well as the water trapped inside the molecular aggregates (Korolczuk, 1982). The viscosity parameters (K, apparent viscosity at zero shear stress n, the power law factor and o-y, the yield stress) of sodium caseinate have been studied and found to be affected by concentration (Hermansson, 1975), precipitation and solution pH of caseinate (Hayes and Muller, 1961 Korolczuk, 1982), de-naturation (Hayes and Muller, 1961 Canton and Mulvihill, 1982), sodium chloride (Hermansson, 1975 Creamer, 1985), calcium chloride (Hayes and Muller, 1961) and temperature (Korolczuk, 1982). 

Prud homme are about a factor of three larger than the predictions of Eq. (9-55), if Y() and C (Newtonian viscosity plateau at low shear rates, while Eq. (9-55) predicts yield behavior at low shear rates, with a power-law viscosity-shear rate slope of—1. The emulsions of Otsubo and Prud homme are evidently affected to some extent by Brownian motion, which is not accounted for in Eq. (9-55). Further experimental and theoretical work on emulsion rheology will be required to establish general scaling rules for these complex emulsions. 

The volume fraction of the dispersed phase is the most important factor that affects the viscosity of emulsions. When particles are introduced into a given flow field, the flow field becomes distorted, and consequently the rate of energy dissipation increases, in turn leading to an increase in the viscosity of the system. Einstein (24, 25) showed that the increase in the viscosity of the system due to addition of particles is a function of the volume fraction of the dispersed particles. As the volume fraction of the particles increases, the viscosity of the system increases. Several viscosity equations have been proposed in the literature relating viscosity to volume fraction of the dispersed phase. We discuss these equations in a later section. 

Effect of Emulsion Characteristics. As discussed in Chapter 4, the rheology of emulsions is affected by several factors, including the dis-persed-phase volume fraction, droplet size distribution, viscosity of the continuous and dispersed phases, and the nature and amount of emulsifying surfactant present. All of these parameters would be expected to have some effect on flow behavior of the emulsion in porous media. However, the relationship between bulk rheological properties of an emulsion and its flow behavior in porous media is feeble at best because, in most cases, the volume... 

The viscosity of the emulsion phases, especially the viscosity of the continuous phase (this is a very significant factor and affects efficiency of petroleum drying by affecting transport of droplets or particles through the medium) ... 

Another important parameter affecting emulsions is the surfactant concentration that affects surface chemistry. This factor was tested for reverse water-in-oil emulsion. The oil phase was simply commercially available car-lubricating oil diluted twice with paint thinner in order to reduce the viscosity of the final sample. Figure 12 illustrates results for emulsions prepared with 6% by weight of water. 

Fenouillot et ol. [368] reviewed polymer blends with solid nanopartides. The authors briefly discussed oil/water emulsions with solid colloidal partides, considering their wettability and location. Next, polymer blends with nanopartides were discussed, starting with systems near the phase separation, and then within the immiscibility region. Some similarities and differences between the low- and high-viscosity emulsions were highlighted. The particular reason for preparing the review seems to be the authors search for factors that may affect nanoparticle localization at the thermodynamic equilibrium. Diverse polymer blends with pseudo-spherical... 

At an applied level, study of the rheology of emulsions is vital in many industrial applications of personal care products. It is useful to summarize the factors that affect emulsion rheology in a qualitative way. One of the most important factors is the volume fraction of the disperse phase, ( ). In very dilute emulsions (( )< 0.01), the relative viscosity, Tir, of the system may be related to ( ) using the simple Einstein equation (as for solid/ liquid dispersions) (15) i.e.. 

Another factor that may affect the rheology of emulsions is the viscosity of the disperse droplets. This is particularly the case when the viscosity of the droplets is comparable to or lower than that of the dispersions medium. This problem was considered by Taylor (17), who extended the Einstein hydrodynamic treatment for suspensions for the case of droplets in a liquid medium. Taylor (17) assumed that the emulsifier film around the droplets would not prevent the transmission of tangential and normal stresses form the continuous phase to the disperse phase and that there was no slippage at the o/w interface. These stresses produce fluid circulation within the droplets, which reduces the flow patterns around them. Taylor derived the following expression for 11 ... 

The third factor that affects emulsion rheology is the droplet size distribution. This is particularly the case at high volume fractions. When rj) > 0.6, 7 is inversely proportional to the reciprocal of the mean droplet diameter [4ff]. The above equations do not show any dependence on droplet size and an account should be made for this effect by considering the average distance between the droplets in an emulsion. At high shear rate, the droplets are completely deflocculated (i.e. all structure is destroyed) and they are equidistance from each other. At a critical separation between the droplets, which depends on droplet size, the viscosity shows a rapid increase. The average distance of separation between the droplets, hm, is related to the droplet diameter, dm, by the simple expression. 

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