Rheological properties shear strength

Rheological Properties shear strength, viscosity Structure polarity Thermal Properties... 

The existence of yield stress Y at shear strains seems to be the most typical feature of rheological properties of highly filled polymers. A formal meaing of this term is quite obvious. It means that at stresses lower than Y the material behaves like a solid, i.e. it deforms only elastically, while at stresses higher than Y, like a liquid, i.e. it can flow. At a first approximation it may be assumed that the material is not deformed at all, if stresses are lower than Y. In this sense, filled polymers behave as visco-plastic media with a low-molecular and low-viscosity dispersion medium. This analogy is not random as will be stressed below when the values of the yield stress are compared for the systems with different dispersion media. The existence of yield stress in its physical meaning must be correlated with the strength of a structure formed by the interaction between the particles of a filler. 

It is evident that for a profound understanding of the rheological properties of fruned silica dispersion at rest and under shear conditions, detailed information about the nature and strength of the interparticulate interaction forces is indispensable. 

Hoglund, E. (1989) The Relationship between Lubricant Shear Strength and Chemical Composition of the Base Oil, Wear 130, 213-224 Astrom, H. and Hoglund, E. (1990) Rheological Properties of Six Greases and their Two Base Oils, Technical Report, Lulea University of Technology, Sweden. 

Experiments were conducted at room temperature. Water was used as the Newtonian fluid. Non-Newtonian liquids included aqueous solutions ofXanthan gum (Keltrol T, Kelco-Merck) as shear-thinning fluids. Solutions were prepared at constant ionic strength by adding 0.1% (w/v) NaCl. These fluids were selected because they had similar rheological properties to several anaerobic media [6-9] and they are clear fluids that allowed flow pattern visualizations. 

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