Viscosity of emulsion

The use of poly(vinyl acetate) or copolymer emulsions eliminates the need for expensive, flammable, odorous, or toxic solvents and the need for the recovery of such solvents. They are easy to apply and the equipment is easy to clean with water, if done promptly. Emulsions also offer the advantage of high sohds content with fluidity, siace the viscosity of emulsions are iadependent of the molecular weight of the resia iu the particles. 

The use of the nomograph is as follows Find the intersecting point of the curves of continuous phase and dispersed phase viscosities on the binary field (left side of nomograph). A line is drawn from this point to the common scale volume fraction of dispersed phase and continuous phase liquids. The intersection of this line with the Viscosity of Emulsion scale gives the result. 

Table IV. Viscosity of emulsions prepared from pea protein...

The viscosity of emulsions obtained from two mutually incompatible polymers dissolved in a common solvent was studied by a falling ball viscometer, a cone-plate viscometer, and a capillary viscometer. The two polymers are polyacrylonitrile and polyurethane, and the solvent is N-methyl-pyrrolidone. The measurements are compared with theory, and a model is proposed for the development of a stationary pressure flow of an emulsion in a capillary. 

Figure 4. Measurements with a falling-ball viscometer. Ratio between viscosities of emulsions and matrix vs. volume fraction of dispersed PAN solutions.

Falling-Ball Viscometer. Taylor (5) has developed a formula for the viscosity of emulsions ... 

Similar dependences for describing the viscosity of emulsions on the basis of the volume averaging method were derived by Mellema and Willemse [60]. They took into account the contribution to the effective viscosity of the interphase tension and obtained a general expression, different from (52) ... 

Viscosity of Emulsions. The viscosity of an emulsion, defined as the ratio of shear stress to shear rate, depends upon several factors ... 

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. 

Shear rate influences the viscosity of emulsions quite significantly when their behavior is non-Newtonian. As discussed earlier, in the low range, emulsions exhibit a Newtonian behavior, and consequently shear rate does... 

The chemical nature and the concentration of an emulsifying agent also play a role in determining the viscosity of emulsions (37). The average particle size, particle size distribution, and the viscosity of the continuous phase (to which an emulsifier is normally added) all depend upon the properties and concentration of emulsifying agent. Also, ionic emulsifiers introduce electroviscous effects, leading to an increase in the emulsion viscosity. 

The viscosity of emulsions is a strong function of temperature it decreases with the increase in temperature (J8). The decrease in emulsion viscosity that occurs with raising the temperature is mainly due to a decrease in the continuous-phase viscosity. The increase in temperature may also affect the average particle size and particle size distribution. When the apparent viscosity of an emulsion (at a given shear rate) is plotted as a... 

Figure 16. Variation of the viscosity of emulsion-solids mixtures with shear stress at different solids volume fraction. (Reproduced with permission from reference 57. Copyright 1991 Pergamon Press.)...

Effects of Solids Shape. The viscosities of emulsion-solids mixtures are compared when irregular-shaped silica sand and spherical glass beads are added separately to an oil emulsion. The results are shown in Figure 18 for different sizes of glass beads and silica sand for synthetic oil. 

Several equations for the viscosity of emulsion systems take the form... 

At the same total Na+ concentration, the viscosities of emulsions made from 3.0 x 10 mole NaOH/gram oil are always less than those from 4.0 x 10. This may be due to the fact that 4.0 x 10 emulsions have a higher concentration of surfactant and smaller particle sizes than 3.0 x 10 emulsions. These two factors induce higher apparent volume fractions as shown on Table II. 

Although finely divided insoluble solid particles constitute an important class of emulsifying agents [44-46], the preparation of liquid-liquid dispersions traditionally involves the use of ionic and nonionic small-molecule surface-active agents. Mixtures of surfactants can also be used to achieve a desirable viscosity of emulsions [12] and to enhance the stabilization properties compared to the effect of one of the emulsifiers [47-49], although evidence of synergistic effects are not always found. 

Figure 7.8. Intrinsic viscosity of emulsion vs. the viscosity ratio (defined in the Figure) [Oldroyd, 1953, 1955].

For the relative viscosity of emulsions, in the absence of deformation and coalescence, Eqs 7.24-7.30 may also be used, provided that the intrinsic viscosity is calculated from Eq 7.50 and that the maximum packing volume fraction is treated as an adjustable parameter, dependent on the interphase. This pragmatic approach has been successfully used to describe [r]] vs. (() variation for such complex systems as industrial lattices (at various stages of conversion), plastisols and organosols. 

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