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Reza Foudazi, Irina Masalova, Alexander Malkin
The rheology of binary mixtures of highly concentrated emulsions

Appl. Rheol. 21:2 (2011) 25326 (3 pages)

The rheological parameters (elastic modules and the yield stress) of binary mixtures of highly concentrated emulsions with different droplet sizes can be several times lower than additive values in a certain range of concentration. This is related to the proper packing of small droplets between larger ones without compression of droplets. While the yield stress is practically absent for these uncompressed droplets, the rather high storage modulus demonstrates the significance of interdroplet interaction in this system.

Cite this publication as follows:
Foudazi R, Masalova I, Malkin A: The rheology of binary mixtures of highly concentrated emulsions, Appl. Rheol. 21 (2011) 25326.

Reza Foudazi, Irina Masalova, Alexander Malkin
Effect of interdroplet interaction on elasticity of highly concentrated emulsions

Appl. Rheol. 20:4 (2010) 45096 (10 pages)

We present a model for osmotic pressure and shear modulus of highly concentrated emulsions by including the interdroplet interaction in terms of disjoining pressure. The results show that even a small addition in interdroplet interaction can lead to significant deviations from the classical Princen-Lacasse-Mason models that take into account only the surface energy as the sole source of elasticity. The newly proposed model predicts new effects, in particular the possibility of nonlinear dependency of elastic modulus on the droplet size, and can be used to discuss the elasticity sources of highly concentrated emulsions. In the second part of this article, the unusual elasticity of highly concentrated explosive emulsions is discussed by using the proposed model.

Cite this publication as follows:
Foudazi R, Masalova I, Malkin A: Effect of interdroplet interaction on elasticity of highly concentrated emulsions, Appl. Rheol. 20 (2010) 45096.

Reza Foudazi, Hossein Nazockdast
Rheology of Polypropylene/Liquid Crystalline Polymer Blends: Effect of Compatibilizer and Silica

Appl. Rheol. 20:1 (2010) 12218 (9 pages)

The effect of classical compatibilizers and silica fillers, which are a new potential type of compatibilizers, on the rheological properties of PP/LCP blends was investigated.The frequency sweep, shear stress growth and stress relaxation upon cessation of steady shear were performed to probe the effect of the interfacial modification and the role of silica, on the rheological behaviour of the blend. It was found that SEBS-g-MA improves the interfacial interaction more than SEBS due to the possible chemical bonding between maleic anhydride groups and LCP chains. The results showed while the hydrophilic silica fills both matrix and the LCP dispersed phases, the hydrophobic silica has some compatibilizing effect on PP/LCP blend samples.

Cite this publication as follows:
Foudazi R, Nazockdast H: Rheology of Polypropylene/Liquid Crystalline Polymer Blends: Effect of Compatibilizer and Silica, Appl. Rheol. 20 (2010) 12218.

Irina Masalova, Alexander Ya. Malkin, Reza Foudazi
Yield stress as measured in steady shearing and in oscillations

Appl. Rheol. 18:4 (2008) 44790 (8 pages)

The yield stresses of five samples (two highly concentrated emulsions, two Kaolin dispersions and mayonnaise) were determined in two ways. In one case, steady shear experiments were performed over a range of incrementally decreasing shear rates. The resulting flow curves, plotted as shear stress against shear rate, clearly showed the existence of a yield stress for each sample, the Herschel-Bulkley model being fitted to obtain values. In the second case, oscillatory amplitude sweeps were performed at three frequencies, and the .dynamic yield stress. was defined as the stress at which deviation from linearity occurred; this procedure has often been used to determine the yield stress of emulsions. It was found that the dynamic yield stress is frequency dependent, and cannot therefore be thought of as physically meaningful material property. At no frequency did the dynamic yield stress correlate with the yield stress obtained from the flow curves.

Cite this publication as follows:
Masalova I, Malkin AY, Foudazi R: Yield stress as measured in steady shearing and in oscillations, Appl. Rheol. 18 (2008) 44790.


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