Viscosity structural

Structural viscosity-the decrease of apparent viscosity with increasing shear stress-is related to the solid-solid aggregation of clay partides as a response to 

If the structure of the viscoelastic suspension changes during flow (as discussed above), the shear stress T is a nonlinear function of the shear deformation rate (dy/dt), expressed by the general relationship  

In this case, the apparent viscosity rj is defined as the slope of the t versus dy/dt line and yields 

If /3 1, the materials are termed pseudoplastic, and their viscosity decreases with the rate of shear deformation as the structure of the flowing material gradually becomes more ordered. If /3 1, the material displays so-called Bingham behavior (see Section 2.4.1.3), and the viscosity increases with increasing shear deformation rate. Such systems are also characterized by a yield stress 6 below which there is no deformation (shear deformation rate D = 0).lf P=l, ideal Newtonian behavior is observed, with a= rj. 

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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 typical viscous behavior for many non-Newtonian fluids (e.g., polymeric fluids, flocculated suspensions, colloids, foams, gels) is illustrated by the curves labeled structural in Figs. 3-5 and 3-6. These fluids exhibit Newtonian behavior at very low and very high shear rates, with shear thinning or pseudoplastic behavior at intermediate shear rates. In some materials this can be attributed to a reversible structure or network that forms in the rest or equilibrium state. When the material is sheared, the structure breaks down, resulting in a shear-dependent (shear thinning) behavior. Some real examples of this type of behavior are shown in Fig. 3-7. These show that structural viscosity behavior is exhibited by fluids as diverse as polymer solutions, blood, latex emulsions, and mud (sediment). Equations (i.e., models) that represent this type of behavior are described below. 

Figure 3-7 Some examples of structural viscosity behavior.

Consider each of the fluids for which the viscosity is shown in Fig. 3-7, all of which exhibit a structural viscosity characteristic. Explain how the structure of each of these fluids influences the nature of the viscosity curve for that fluid. 

More recently, Yang and Thompson implemented this type of sensor in FI manifolds, which they consider ideal environments for relating the sensor s hydrodynamic response to the analyte s concentration-time profile produced by the dispersion behaviour of sample zones. Network analysis of the sensor generates multi-dimensional information on the bulk properties of the liquid sample and surface properties at the liquid/solid interface. The relationship between acoustic energy transmission and the interfacial structure, viscosity, density and dielectric constant of the analyte have been thoroughly studied by using this type of assembly [171]. 

The Eyring flow shows a typical dependence upon stress. With increasing stress the viscosity r decreases (structural viscosity). The calculations are in good agreement with the experimental values. Figures 21 and 22 show the influence of shearing stress on the viscosity. 

If the internal phase in an emulsion has a sufficiently high volume fraction (typically anywhere from 10 to 50%) the emulsion viscosity increases due to droplet crowding, or structural viscosity, and becomes non-Newtonian. The maximum volume fraction possible for an internal phase made up of uniform, incompressible spheres is 74%, although emulsions with an internal volume fraction of 99% have... 

Since wet foams contain approximately spherical bubbles, their viscosities can be estimated by the same means that are used to predict emulsion viscosities. In this case the foam viscosity is described in terms of the viscosity of the continuous liquid phase (tjo) and the amount of dispersed gas (4>). In dry foams, where the internal phase has a high volume fraction the foam viscosity increases strongly due to bubble crowding, or structural viscosity, becomes non-Newtonian, and frequently exhibits a yield stress. As is the case for emulsions, the maximum volume fraction possible for an internal phase made up of uniform, incompressible spheres is 74%, but since the gas bubbles are very deformable and compressible, foams with an internal vol-... 

The high structural viscosity of bimodal products means that advanced modeling methods are needed to optimize the pressure build-up zones. Calculation and evaluation of dimensionless parameters helps to keep the complexity within limits. 

Dolby, R.M. 1941b. The rheology of butter. II. The relation between rate of shear and shearing stress. The effect of temperature and of reworking on hardness and on structural viscosity. J. Dairy Res. 12, 337-343. 

The fact that the melt of the block copolymer above a critical shear stress shows the same structure-viscosity relations as found for linear melts in simple shear flow is taken as an indication of a monomolecular melt state. 

Relative to secondary structure, viscosity, sedimentation velocity, ultraviolet difference spectra and optical rotatory dispersion studies (4,24,25) showed that glutenin appears to be an assymetric molecule with a low a-helix content (10-15%). Glutenin contained more a-helix structure in hydrochloric acid solutions and less in urea solutions. The amount of a-helix structure is also influenced by changes in ionic strength (26). 

The critical analysis of the results on foam rheology, proposed by Heller and Kuntamukkula [16], has shown that in most of the experiments the structural viscosity depends on the geometrical parameters of the device used to study foam flow. This means that incorrect data about flow regime and boundary conditions, created at the tube and capillary walls, etc., are introduced in the calculation of viscosity (slip or zero flow rate). Most unclear remains the problem of the effect of the kind of surfactant and its surface properties on foam viscosity and on the regime of foam flow (cross section rate profile and condition of inhibition of motion at the wall surface). 

Polymerizable systems, like the metal alkoxides, are interesting because it is possible to form all of these different film structures by simply manipulating the solution chemistry. Properties such as structure, viscosity, and concentration are easily controlled with polymers. 

Mizrahi, S. 1979. A review of the physicochemical approach to the analysis of the structural viscosity of fluid food products.. 7. TextureStud. 10 67-82. 

We see therefore the chain molecule loses its central symmetry and is elongated statistically in the direction of 3r/4 and compressed in the direction of 3 c/4. Such a deformation is the source of structural viscosity. 

Therefore, if the chain is stiU spherical as can be judged from the absence of a structural viscosity we are led to an expression... 

To show this structure viscosity we measured the intrinsic viscosity of the same polymer solutions in viscometers with different capillary lumen (Table III). The lumen had a strong influence on the measured values the greater it was, the smaller were the figiu es for the intrinsic viscosity. 

FIGURE 8.7 Non-Newtonian flow behavior, a Structural viscosity (for high molecular solution). b Dilatant flow (suspension with high concentration), c Viscoplastic with flow limits 1, ideal plastic 2 or 3, nonlinear plastic flow, d 1, thixotropy flow 2, antithixotropy flow 3, viscoelastic flow e rheopexy flow. 

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