Viscosity of water-in-oil emulsions

Figure 8. Viscosity of water-in-oil emulsions Formulation B, 2.91 poise...

Viscosity of w/o Emulsions. The viscosity of water-in-oil emulsions at infinte shear depends on several factors ... 

Sherman, P. 1955c. Studies in oil-in-water emulsions. IV. The influence of the emulsifying agent on the viscosity of water-in-oil emulsions of high water content. J. Colloid Sci. 10,... 

Sherman [36] reported that the viscosity of water-in-oil emulsions stabilized with nonionic surfactants falls with time. Refer to Fig. 38. This phenomenon is controlled by the increase in the particle size caused by coalescence. The flocculation and coalescence rates will cause either the increase or decrease of the viscosity on aging [37]. 

Finally, permeability reductions attributed in the literature to the formation of water-in-oil emulsions are evidently caused by the high viscosity of those emulsions or to the formation of an oil film (lamella) across the pore throat (9). 

The presence of emulsifiers (materials that promote emulsion formation) influences the ability to form an emulsion between petroleum and water. Emulsifiers act by lowering the interfacial tension between the phases and creating a strong adsorbed layer around the surface of the internal phase. Emulsifiers that are soluble in water (hydrophilic) promote the creation of oil in water emulsion. Alkaline soaps, starch and so on are such hydrophilic emulsifiers. Hydrophobic emulsifiers (i.e. soluble in petroleum) promote the formation of water in oil emulsions. Hydrophobic emulsifiers include resins dispersed in particle form within soot, clay and other substances. Petroleum emulsions can be characterized using properties such as viscosity, dispersion, density, electrical properties and stability. The viscosity of petroleum emulsion changes within wide ranges and depends on the viscosity of petroleum, temperature, and amounts of petroleum and water. 

Emulsification Emulsification is considered the second most important weathering process after a marine spill by which water is dispersed into oil in the form of small droplets. The mechanism of water-in-oil emulsion formation is not yet fully understood, but it probably starts with sea energy forcing the entry of small water droplets, about 10 to 25 /rm in size, into the oil. Emulsions of many types contain about 70% water. In general, water-in-oil emulsion can be categorized into four types (1) unstable oil simply does not hold water (2) entrained water droplets are simply held in the oil by viscosity to form an unstable emulsion, and it breaks down into water and oil within minutes or a few hours at most (3) semistable or meso-stable the small droplets of water are stabilized to a certain extent by a combination of the viscosity of the oil and interfacial action of asphaltenes and resins. For this to happen, the asphaltenes or resin content of the oU must be at least 3% by weight. The viscosity of meso-stable emulsions is 20 to 80 times... 

Matsumoto, S., and Kohda, M., 1980, The viscosity of water-in-oil-in-water emulsions An attempt to estimate the water permeation coefficient of the oil layer from the viscosity changes in diluted systems on ageing under osmotic pressure gradients, J. Colloid Interface 73 13-20. 

As described earlier in the section on bead or suspension polymers (Section 3.3.1.2), a solution of monomer(s) is prepared in water and then mixed into a low to medium viscosity non-volatile oil phase. In this process, which is often referred to as an inverse emulsion polymerisation technique, surfactants which promote the formation of water-in-oil emulsions are commonly used. These would usually be materials with an HLB (hydrophihc-lipophilic balance) value in the range 4—7, an example of which is sorbitan mono-oleate. In order to achieve the desired droplet particle size of a maximum around 1 pim prior to polymerisation, high shear homogenisers are used to assist the formation of such very small... 

Figure 12.1 Viscosity behavior of water-in-oil emulsions containing PEG7-hydrogenated castor oil/dicaprylyl ether/decyl oleate/glycerol/MgS04 = 3.5 7 7 5 0.7 as a function of water content (Reproduced by permission of Allured from ref 7)...

The viscosity function of the natural gums is utilized in both oil in water and water in oil emulsions. Often the gums are referred to as emulsifying agents. They are considered not so much as emulsifiers, but rather as emulsion protectors or stabilizers. To a large extent, the function is to increase the viscosity of the aqueous phase so that it approaches, or slightly exceeds, that of the oil hence, there is less tendency for the two phases, once emulsified, to separate by mechanical slippage. 

Our goal is to develop a property-performance relationship for different types of demulsifiers. The important interfacial properties governing water-in-oil emulsion stability are shear viscosity, dynamic tension and dilational elasticity. We have studied the relative importance of these parameters in demulsification. In this paper, some of the results of our study are presented. In particular, we have found that to be effective, a demulsifier must lower the dynamic interfacial tension gradient and its ability to do so depends on the rate of unclustering of the ethylene oxide groups at the oil-water interface. 

For effective demulsification of a water-in-oil emulsion, both shear viscosity as well as dynamic tension gradient of the water-oil interface have to be lowered. The interfacial dilational modulus data indicate that the interfacial relaxation process occurs faster with an effective demulsifier. The electron spin resonance with labeled demulsifiers suggests that demulsifiers form clusters in the bulk oil. The unclustering and rearrangement of the demulsifier at the interface may affect the interfacial relaxation process. 

This water-in-oil emulsion is smooth and non-greasy. The Ritahydrox produces a stable product, which allows for the addition of other materials, if desired. The emulsion will tighten and the viscosity will increase as the Ritahydrox level is raised (to about the 1% level). 

Some special problems arise at sea. When crude oil is spilled on the ocean, a slick is formed which spreads out from the source with a rate that depends on the oil viscosity. With sufficient energy an O/W emulsion may be formed, which helps disperse oil into the water column and away from sensitive shorelines. Otherwise, the oil may pick up water to form a water-in-oil emulsion, or mousse ( chocolate mousse ). These mousse emulsions can have high water contents and have very high viscosities, with weathering they can become semi-solid and considerably more difficult to handle, very much like the rag-layer emulsions referred to above. The presence of mechanically strong films makes it hard to get demulsifiers into these emulsions, so they are hard to break. See Chapter 9. 

The highly viscous spray fluids used in pesticide application have been either water-in-oil emulsions or solutions of macromolecules both systems are non-Newtonian since their viscosity varies with the applied shear. While a viscosity parameter which is suitable for studies on drop formation was subsequently devised for such systems (II), it was necessary to use Newtonian liquids in the initial studies on the effect of viscosity on drop size. Sugar solutions behave as Newtonian liquids and provide a suitable means of varying viscosity over a wide range. These were prepared from a commercially available syrup by dilution with distilled water 1% w/v of a black dye (Nigrosine G140) was added to each solution to render the spray drops visible for sizing. 

Application of the Theory to w/o Emulsions. Since concentrated w/o emulsions are non-Newtonian fluids, the viscosity of the emulsion is meaningless unless it is related to shear rate under which the measurement is made. The viscosity of concentrated emulsions decreases as the shearing forces to which they are subjected increases this is shown in Figure 8 for three typical water-in-oil emulsions. However, at very high and very low shear rates they have limiting shear-independent viscosities, which may be designated 77, and rj0, respectively. 

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. 

Sherman, P. 1955a. Studies in water-in-oil emulsions. Part 5. The influence of internal phase viscosity on the viscosity of concentrated water-in-oil emulsions. Kolloid Z., 141, 6-11. 

This can be useful when one needs to prepare an emulsion with a very high volume weight of dispersed phase for example, a water-in-oil emulsion for a sauce. Such an emulsion can be rather thick in consistency (high viscosity). By first preparing an oil-in-water emulsion (with a low volume of oil in the water phase), and then pressing it through a hydrophobic membrane, one can very easily make a thick water-in-oil emulsion. 

Microemulsion Polymerization. Polyacrylamide microemulsions are low viscosity, nonsettling, clear, thermodynamically stable water-in-oil emulsions widi particle sizes less dian about 100 nm (98—100). They were developed to try to overcome the inherent settling problems of die larger particle size, conventional inverse emulsion polyacrylamides. To achieve the smaller microemulsion particle size, increased surfactant levels are required, making diis system more expensive dian inverse emulsions. Acrylamide microemulsions form spontaneously when the correct combinations and types of oils, surfactants, and aqueous monomer solutions are combined. Consequendy, no homogenization is required. Polymerization of acrylamide microemulsions is conducted similarly to conventional acrylamide inverse emulsions. To date, polyacrylamide microemulsions have not been commercialized, aldiough work has continued in an effort to exploit die unique features of diis teclmology (100). 

Water-in-oil emulsions, generally appear to be black, do not dilute with water, and have electrical conductivity lower than that of the brine. The viscosities may be very high, and the shear behavior is thixotropic. 

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