Rheology, emulsion

Liquid-in-liquid systems can be divided into three categories those in which both liquids are Newtonian, those in which both phases are viscoelastic, and systems consisting of one Newtonian and one viscoelastic liquid. The first of these categories are emulsions, E, the second polymer blends, B, and the third undefined class of system is usually used as a model, M, for gaining insight into the effects of elasticity on flow and morphology. Some polymer blends may also be type M. 

Several reviews on the emulsion rheology have been published [65, 89,100-109]. Emulsions containing a high volume fraction of the dispersed phase, 0.74, have been reviewed by Cameron and Sherrington ]110]. Emulsions as models for flow of polymer blends and alloys have been discussed by Utradd [1, 4]. 

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 

Newtonian Flow Einstein s treatment of suspensions was extended to emulsions by Oldroyd [111, 112], who incorporated the effects of interphase  

Starting with cell model of creeping flow, Choi and Schowalter [113] derived a constitutive equation for an emulsion of deformable Newtonian drops in a Newtonian matrix. The authors characterized the interphase with an ill-defined interfacial tension coefficient, Vu, affecting the capillarity number, k = (Judfvu. The analysis indicated that depending on magnitude of /cy the emulsion may be elastic, characterized by two relaxation times. For the steady-state shearing, the authors expressed the relative viscosity of emulsions and the first normal stress difference as  

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Rheo-NMR [86] methods have been shown to be well-suited to emulsion rheology studies [28] and could be combined with any of the topics described above. The combination of structural and rheological measurements is a promising area for further research. 

PE Miner. Emulsion rheology creams and lotions. In D Laba, ed. Rheological Properties of Cosmetics and Toiletries. New York Marcel Deklcer, 1993, pp 313-370. 

R Michaut, P. Perrin, and P. Hebraud Interface Composition of Multiple Emulsions Rheology as a Probe. Langmuir 20, 8576 (2004). 

Miner, P.E. Emulsion Rheology Creams and Lotions in Rheological Properties of Cosmetics and Toiletries, Laba, D. (Ed.), Marcel Dekker New York, 1993, pp. 313-370. 

Micronization is an optional process that helps to reproduce the fatty sensation afforded by polysaccharides. The 0.2-nm particles in Avicel (FMC, 1993) and the 1-5-nm particles in the rice mimetic (Pszczola, 1991) simulate lipid emulsion rheology as well as lipid oral sensations. The simulation mechanism implicates a weak gel structure and an expansive surface where a large volume of water is immobilized. 

Many epoxy dispersions are compatible with most types of latex emulsions including acrylic, urethane, styrene butadiene, vinyl chloride, and polyvinyl acetate. The epoxy dispersion can be used as a modifier for these emulsions to alter handling and application characteristics such as emulsion rheology, foaming tendencies, pH sensitivity, wetting properties, and coating coalescence. They can also be reacted into the latex resin either by reacting the epoxy with a functionalized latex or by use of an epoxy with a coreactant. In this way adhesive systems can be formulated that are cured at room or elevated temperatures. 

Colloidal interactions between emulsion droplets play a primary role in determining emulsion rheology. If attractions predominate over repulsive forces, flocculation can occur, which leads to an increase in the effective volume fraction of the dispersed phase and thus increases viscosity (McCle-ments, 1999). Clustering of milk fat globules due to cold agglutination increases the effective volume fraction of the milk fat globules, thereby increasing viscosity (Prentice, 1992). 

Mathematical Modeling of Emulsion Rheology Food emulsions are compositionally and structurally complex materials that can exhibit a wide range of different rheological behavior, ranging from low-viscosity fluids (such as milk... 

Factors Influencing Emulsion Rheology A variety of factors determine the rheological properties of food emulsions. Some of the most important of these factors are highlighted below. 

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. 

When using stable, dilute Newtonian emulsions through porous media, the flowing permeability, fcf, must be used in Darcy s law to describe its behavior instead of the initial or conventional permeability. When plugging due to the flow of Newtonian macroemulsions occurs, only the permeability of the porous medium should be adjusted. Emulsion rheology with respect to Newtonian and non-Newtonian behavior will be reviewed under the section Mathematical Models of Emulsion Flow in Porous Media . 

Tadros, T.F., Fundamental principles of emulsion rheology and their applications, in Proc. Eirst World Congress on Emulsion, 19-22 Oct., Paris, 1993, p. 237. 

Lequeux F. Emulsion rheology. Current Opinion Colloid Interface Sci 1998 3 408-411. 

Emulsion rheology Emulsion-like behavior Encapsulation End-to-end distance Energy (high) of irradiation Energy density, cohesive, (CED)... 

Tadros summarized the fundamental prineiples of emulsion rheology (61). Emulsions stabilized by surfactant films (such as resins and asphaltenes) behave like hard sphere dispersions. These dispersions display viscoelastic behavior. Water-in-oil emulsions show a transition from predominantly viscous to predominantly elastic response as the frequency of oscillation exceeds a critical value. Thus, a relaxation time can be determined for the system which increases with the volume fraction of the discontinuous phase. At the critical value, the system shows a transition from predominantly viscous to predominantly elastic response. This reflects the increasing steric interaction with increases in volume of the discontinuous phase. 

In 1996, Pal studied the effect of droplet size and found it had a dramatic influence on emulsion rheology (62). Fine emulsions have much higher viscosity and storage moduli than the corresponding coarse emulsions. The shear thinning effect is much stronger in the case of fine emulsions. Water-in-oil emulsions age much more rapidly than oil-in-water emulsions. More recently, Lee et al. (63) and Aomari et al. (64) examined model emulsions and found that a maximum shear strain existed which occurred around 100s. ... 

Some systematic studies indieated that the previously known dependence of emulsion rheology on internal phase content and drop size charaeteristies eould be applied to pe-troleum-in-water emulsions (48). However, most early studies were not concerned with the presence of stabilizing substances like surfactants (49—51), so that they were missing an extremely important issue in practice. 

The study of emulsion rheology was pioneered by Geoffr Taylor (1,2), who not only experimentally identified e dimensionless groups (capillary number and viscosity ratio) that control droplet deformation in an emulsion in simple shear and hyperboUc flow fields, but also proposed a linear theory for droplet deformation in flow. The droplet Cs illary number is defined as Ca f -... 

Tadros, Th.F. (1994) Fimdamental principles of emulsion rheology and then-applications. Colloids Surf. A Phydcochem. Eng. Aspects, 91, 39-55. 

Lequeux, F. (1998) Emulsion rheology. Curr. Opin. CdBoid Itdafiice Sd 3 (4). 408-411. 

Effects of droplet deformability on emulsion rheology. Colloids Surf. A Physicochem. Eng. Aspects, 299 (1-3), 65-72. 

The proceedings cover six major areas of research related to chemical flooding processes for enhanced oil recovery, namely, 1) Fundamental aspects of the oil displacement process, 2) Microstructure of surfactant systems, 3) Emulsion rheology and oil displacement mechanisms, 4) Wettability and oil displacement mechanisms, 5) Adsorption, clays and chemical loss mechanisms, and 6) Polymer rheology and surfactant-polymer interactions. This book also includes two invited review papers, namely, "Research on Enhanced Oil Recovery Past, Present and Future," and "Formation and Properties of Micelles and Microemulsions" by Professor J. J. Taber and Professor H. F. Eicke respectively. 

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.. 

The third factor that affects emulsion rheology is the droplet size distribution. This is particularly the case at high-volume fractions. When ( ) > 0.6, T) is inversely proportional to the reciprocal of the mean droplet diameter (18). 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... 

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