Shear thinning viscosity

So far the results have been shown in which the metal alkoxide solutions are reacted in the open system. It has been shown that the metal alkoxide solutions reacted in the closed container never show the spinnability even when the starting solutions are characterized by the low acid content and low water content (4). It has been also shown from the measurements of viscosity behavior that the solution remains Newtonian in the open system, while the solution exhibits structural viscosity (shear-thinning) in the closed system. 

The concentration of lactic acid in the steep has been shown to affect both the yield of starch178 and the quality of the resulting starch.179 Starch yields increased with increasing lactic acid concentration up to —0.5%, and decreased when more than —2% lactic acid was used. Shandera and lackson179 tested starch quality when steeped at 57°C with either 0.2% or 1.5% lactic acid and 0.05% or 0.3% sulfur dioxide. The level of sulfur dioxide had a small effect on starch quality, but the level of lactic acid had a pronounced reduction effect on peak viscosity, shear thinning viscosity, set-back viscosity, pasting viscosity and starch water solubility. 

Since homogenous melts are covered in a later account of pressure build-up and power input in the extruder (Chapter 7), this chapter confines itself to the flow behavior of homogenous unfilled polymer melts and on the introduction of the most important rheological parameters such as viscosity, shear thinning, elasticity, and extensional viscosity. The influence of these rheological properties on simple pressure- and drag flows is demonstrated, while the influence of rheological parameters on pressure build-up and power input in the extruder is described in more detail in Chapter 7. 

As discussed in Sect. 4, in the fluid, MCT-ITT flnds a linear or Newtonian regime in the limit y 0, where it recovers the standard MCT approximation for Newtonian viscosity rio of a viscoelastic fluid [2, 38]. Hence a yrio holds for Pe 1, as shown in Fig. 13, where Pe calculated with the structural relaxation time T is included. As discussed, the growth of T (asymptotically) dominates all transport coefficients of the colloidal suspension and causes a proportional increase in the viscosity j]. For Pe > 1, the non-linear viscosity shear thins, and a increases sublin-early with y. The stress vs strain rate plot in Fig. 13 clearly exhibits a broad crossover between the linear Newtonian and a much weaker (asymptotically) y-independent variation of the stress. In the fluid, the flow curve takes a S-shape in double logarithmic representation, while in the glass it is bent upward only. 

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. 

The following refers to moderate viscosity, shear thinning (and sometimes viscoelastic) liquids, in the transitional Reynolds Number regime. 

Thixotropy occurs when clusters of filler particles break up and fluidity increases. At rest, fillers exist in clusters and their strength, size, and shape determine the static viscosity of the adhesive. The total surface area of the filler particles also contributes to static viscosity. Shear thinning occurs when the clusters, such as silver flake in silver-filled epoxies, break apart and viscosity decreases then, as stress is removed, the clusters form again and viscosity increases. ... 

The thickness of the liquid sheet on the drum is independent of the pressure applied between the applicator roller and the drum. It depends largely on the viscosity and the surface tension of the liquid as well as on the ratio of rotational speeds of the drum and roller and the nip width. A stable thickness can be achieved for medium viscosity shear-thinning liquids at moderate Reynolds number. Re (the ratio between momentum and viscous forces), low capillary number, Ca (the ratio of the viscous force and surface tension), and low rotational speed ratio." A smaller Ca (<0.01) or a larger surface tension extends coating stability to higher rotation speeds. A stable sheet is established between a minimum and a maximum drum speed and at a critical ratio of rotational speeds of the applicator roller and the drum. The sheet formed beyond the eritical point is unstable, leading to ribbing and may entrain air bubbles as well especially if the liquid contains excessive surfactants." This rarely occurs in drum dryer operation because both the rotation speed and the ratio of rotation speeds are low (linear speed of drum surface rarely exceeds 0.3 m/s). 

Figure 8.22 Typical relationship between hold-up and power input when dispersing gas in a high viscosity, shear-thinning fluid (a) A single disc turbine (b) A combination of 45° downward pumping impeller and disc turbine...

Koenderink, et al. examined the motion of perfluorinated hydrocarbon spheres through xanthan solutions(72). Depolarized QELSS spectra were measured at a series of angles and fitted to second-order cumulant expansions. The spheres had radius 92.5 nm the xanthan molecular weight was 4 MDa. Koenderink, et al. measured solution viscosity, shear thinning, storage and loss moduli, translational and rotational diffusion coefficients Dp and Dr of the probes, and probe sedimentation coefficient s, and made an extensive and systematic comparison... 

This is one of the most important functional tests for starches because aft analyzing the pasting curve, temp uture at start of gelatinization, peak viscosity, shear thinning, and setback viscosity (retrogradation) can be determined. These properties greatly influence processing characteristics and quality of end products. 

Zero-shear viscosity Shear-thinning exponent Upper and lower Newtonian Random coil strnctnre Relaxation time End-to-end distance Deborah nnmber Weissenberg nnmber Constitntive eqnation Power-law llnid Ellis model Cross model... 

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