Viscoelastic behavior shear-thickening viscosity

This chapter is an in-depth review on rheology of suspensions. The area covered includes steady shear viscosity, apparent yield stress, viscoelastic behavior, and compression yield stress. The suspensions have been classified by groups hard sphere, soft sphere, monodis-perse, poly disperse, flocculated, and stable systems. The particle shape effects are also discussed. The steady shear rheological behaviors discussed include low- and high-shear limit viscosity, shear thinning, shear thickening, and discontinuity. The steady shear rheology of ternary systems (i.e., oil-water-solid) is also discussed. 

Most fluids exhibit non-Newtonian behavior—blood, household products like toothpaste, mayonnaise, ketchup, paint, and molten polymers. As shown in Figure 7.9, shear stress, t, increases linearly with strain rate, y, for Newtonian fluids. Non-Newtonian fluids may be classified into those that are time dependent or time independent and include viscoelastic fluids. Shear thinning (pseudoplastic) and shear thickening (dilatant) fluids are time independent while rheopectic and thixotropic are time dependent. The shear stress (viscosity) of shear thinning fluids decreases with increasing shear rate and examples include blood and syrup. The viscosity of dilatant fluids increases with shear rate. The viscosity of rheopectic fluids—whipping cream, egg whites—increases with time while thixotropic fluids— paints (other than latex) and drilling muds— decrease their viscosity with the duration of the shear. 

Usually, sols behave as Newtonian liquids, when the viscosity is low due to low concentration of particles, small particle size and/or separated particles. On the other hand, when the viscosity becomes high due to growth or connection of the particles, the sols behave as non-Newtonian liquids, exhibiting viscoelastic properties, such as shear thinning or shear thickening. These behaviors can be found by measuring the viscosity as a function... 

Fig. 8 plots resistance factor vs. flux during injection of many polymer solutions into a 5120-md porous polyethylene core. For polymer concentrations even as low as 25 ppm (one-eighth the value of C ), shear thickening was evident. In contrast, viscosity vs. shear rate showed Newtonian behavior, with a value very close to 1 cp. As described in the literature (Durst et al. 1982), the elongational flow field associated with porous media can accentuate viscoelastic behavior that is not apparent from a pure shear field. This observation provides our first reason to doubt that the transition from Newtonian behavior to shear-thinning behavior in a viscometer correlates directly with the onset of shear thickening in porous media. 

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