Viscoelasticity emulsions

Moschakis, T., Murray, B.S., Dickinson, E. (2005). Microstructural evolution of viscoelastic emulsions stabilized by sodium caseinate and xanthan gum. Journal of Colloid and Interface Science, 284, 714-728. 

Palierne JF (1990) Linear rheology of viscoelastic emulsions with interfacial-tension. Rheol Acta 29 204-214... 

Stokes, J. R., Wolf, B., and Frith, W. J. 2001. Phase-separated biopolymer mixture rheology prediction using a viscoelastic emulsion model. J. Rheol 45 1173-1191. 

For infinitely diluted viscoelastic emulsions, the shear dependence of inherent viscosity was derived as [Barthes-Biesel and Acrivos, 1973] ... 

For infinitely diluted viscoelastic emulsions the shear dependence of inherent... 

Bousmina, M. (1999) Rheology of polymer blends linear model for viscoelastic emulsions. Rheol Acta, 38 (1), 73-83. 

Bousmina, M., Aouina, M., Chaudry, B., Gu nette, R., and Bretas, R.E.S. (2001) Rheology of polymer blends non-linear model for viscoelastic emulsions undergoing high deformation flows. Rheol. Acta, 40 (6), 538-551. 

Palierne JE. Linear rheology of viscoelastic emulsions with interfacial tension. Rheol Acta 1990 214 204-14. Vermant J, Cioccolo G, Golapan Nair K, Moldenaers P. Coalescence suppression in model immiscible polymer blends by nano-sized colloidal particles. Rheol Acta 2004 43 529-38. 

The rheological properties of a fluid interface may be characterized by four parameters surface shear viscosity and elasticity, and surface dilational viscosity and elasticity. When polymer monolayers are present at such interfaces, viscoelastic behavior has been observed (1,2), but theoretical progress has been slow. The adsorption of amphiphilic polymers at the interface in liquid emulsions stabilizes the particles mainly through osmotic pressure developed upon close approach. This has become known as steric stabilization (3,4.5). In this paper, the dynamic behavior of amphiphilic, hydrophobically modified hydroxyethyl celluloses (HM-HEC), was studied. In previous studies HM-HEC s were found to greatly reduce liquid/liquid interfacial tensions even at very low polymer concentrations, and were extremely effective emulsifiers for organic liquids in water (6). 

The surface characteristics of these species are determined by the particulates and stress transfer across the membrane will tend to be low, reducing internal circulation within the drop. The structure of the interface surrounding the drop plays a significant role in determining the characteristics of the droplet behaviour. We can begin our consideration of emulsion systems by looking at the role of this layer in determining linear viscoelastic properties. This was undertaken by... 

E. Dickinson and I. Chen Viscoelastic Properties of Protein-Stabilized Emulsions Effect of Protein-Surfactant Interactions. I. Agric. Food Chem. 46, 91 (1998). 

Perhaps the most important and striking features of high internal phase emulsions are their rheological properties. Their viscosities are high, relative to the bulk liquid phases, and they are characterised by a yield stress, which is the shear stress required to induce flow. At stress values below the yield stress, HIPEs behave as viscoelastic solids above the yield stress, they are shear-thinning liquids, i.e. the viscosity varies inversely with shear rate. In other words, HIPEs (and high gas-fraction foams) behave as non-Newtonian fluids. 

Figure 3.5 Demonstration of correlation between the stickiness of protein-coated droplet pair encounters in shear flow (left ordinate axis) and viscoelasticity of concentrated emulsions (right ordinate axis) with the strength of protein-protein attraction as indicated by the second virial coefficient A2 determined from static light scattering , percentage capture efficiency (0%) A, complex shear modulus (G ) for emulsions stabilized by asl-casein or (3-casein (pH = 5.5, ionic strength in the range 0.01-0.2 M).

Hence, from the previously described light-scattering study of caseinate self-assembly in solution, we can postulate that heating/cooling not only alters the nature and strength of the physical (hydrophobic) interactions between emulsion droplets covered by caseinate. It most likely also transforms the nanoscale structural characteristics of the protein network in the bulk and at the interface, thereby affecting the viscoelastic and microstructural properties of the emulsions. 

Chen, J., Dickinson, E. (1998) Viscoelastic properties of protein-stabilized emulsions effect of protein-surfactant interactions. Journal of Agricultural and Food Chemistry, 46, 91-97. 

Evidence for the flocculation of emulsion droplets is commonly derived from a combination of rheological and creaming stability experiments. For instance, a marked increase in both the viscoelasticity of emulsions of moderately high oil volume fraction (40 vol%) and the rapid serum... 

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