Rheology non-Newtonian behavior

The strongest appeal of NEMD, however, is its scope and versatility. In particular, the technique allows one to compute the rich and varied nonlinear behavior of systems far from equilibrium. This asset has been used to great advantage to study the atomic basis of the rheological non-Newtonian behavior of liquids. There was no practical technique to investigate the rheological properties of fluids from an atomistic viewpoint before NEMD. (Indeed the word rheology was rarely mentioned in a statistical-mechanical context.)... 

Rheology. Both PB and PMP melts exhibit strong non-Newtonian behavior thek apparent melt viscosity decreases with an increase in shear stress (27,28). Melt viscosities of both resins depend on temperature (24,27). The activation energy for PB viscous flow is 46 kj /mol (11 kcal/mol) (39), and for PMP, 77 kJ/mol (18.4 kcal/mol) (28). Equipment used for PP processing is usually suitable for PB and PMP processing as well however, adjustments in the processing conditions must be made to account for the differences in melt temperatures and rheology. 

The rheological properties change behavior, relative to more dilute solutions, above cp = 0.2, where non-Newtonian behavior is then exhibited. The power law dependence of rj on cp is in harmony with the Zimm rather than the Rouse model, which suggests that hydrodynamic interactions between these polymers, in a mean field sense, are important. Electrical properties also begin to deviate for Nafion solutions above cp = 0.2, and mechanical percolation is essentially the same for the sodium and acid forms. 

The presentation in this chapter dwells rather heavily on the classification, measurement, and interpretation of non-Newtonian behavior. These rheological fundamentals have frequently been presented in literature which is unfamiliar to the engineer and have usually included much discussion of factors which at the present time are of minor engineering interest. Accordingly, it was felt that one of the primary needs in this field was a concise summary of these fundamentals and common definitions. It is hoped that thereby future developments may be undertaken in an orderly and rigorous manner, as contrasted to the relatively fruitless empiricism which has enveloped areas of this field in the past. 

CMCs in the absence of added electrolyte may be greatly influenced by electrovis-cous effects marked decreases in intrinsic viscosity on electrolyte addition have been observed in many cases36). Peculiar and highly interesting rheological properties of surfactant solutions include observations of strongly non-Newtonian behavior as well as of viscoelasticity these are yet incompletely understood. 

The rheological properties show particularly large changes and in many cases the solutions show a non-Newtonian behavior and for a number of cases pronounced viscoelasticity has been demonstrated. That the classification of a certain surfactant depends very much on temperature is probably best illustrated by the viscosity of... 

Solidified milk fat displays non-Newtonian behavior. It acts as a plastic material with a yield value (Sone, 1961 deMan and Beers, 1987). Throughout its wide melting range, milk fat, like butter, exhibits viscoelasticity, possessing both solid and liquid-like characteristics (Sone, 1961 Shama and Sherman, 1968 Jensen and Clark, 1988 Kleyn, 1992 Shukla and Rizvi, 1995). Several models to describe the complex rheological behavior of milk fat have been proposed. Figure 7.12 shows the corresponding stress-strain curves for the models discussed. 

The major characteristic of a polymeric reactor that is different from most other types of reactors discussed earlier is the viscous and often non-Newtonian behavior of the fluid. Shear-dependent rheological properties cause difficulties in the estimation of the design parameters, particularly when the viscosity is also time-dependent. While significant literature on the design parameters for a mechanically agitated vessel containing power-law fluid is available, similar information for viscoelastic fluid is lacking. 

Previous investigations (4, 5,6,7,8) have shown that block copolymers exhibit unusual melt rheological properties such as a very high viscosity, elasticity, and non-Newtonian behavior even at very low shear rates which are all attributed to the multiphase structure resulting from the incompatibility between the two copolymer units in the melt state. 

Emulsion Quality. The quality of an emulsion is defined as the volume fraction (or percent) of the dispersed phase in the emulsion. The quality of emulsions strongly affects their rheology. Several studies have been reported for the relationship of isothermal shear stress to shear rate for emulsions of different qualities. OAV emulsions having qualities less than 0.5 (or 50%) exhibit Newtonian behavior, and those having higher qualities exhibit non-Newtonian behavior (9, 16, 25),... 

When using stable, dilute Newtonian emulsions through porous media, the flowing permeability, fcf, must be used in Darcy s law to describe its behavior instead of the initial or conventional permeability. When plugging due to the flow of Newtonian macroemulsions occurs, only the permeability of the porous medium should be adjusted. Emulsion rheology with respect to Newtonian and non-Newtonian behavior will be reviewed under the section Mathematical Models of Emulsion Flow in Porous Media . 

As discussed earlier, the rheology of emulsions depends on a number of factors, primary among which is the quality. Emulsions with qualities of less than 50% (oil) are considered Newtonian, whereas those having higher qualities exhibit non-Newtonian behavior. 

Let us consider power-law fluids in more detail. Experiments [141] show that the index n of non-Newtonian behavior of a substance may be treated as a constant if the temperature differences in the flow region do not exceed 30 to 50 K. The medium consistence k = k(T) is much more sensitive to temperature inhomogeneities and decreases with increasing T. Therefore, the rheological equation of state for a power-law fluid in the nonisothermal case can be written as follows ... 

Athabasca deposit, the temperature dependence of the viscosity is shown in Figure 6. The Athabasca bitumen rheology is not typical of that in other world locations. For example, the rheology of bitumen in the Utah deposits, which have much higher effective viscosities (48, 49), is more complex and exhibits markedly non-Newtonian behavior (47). 

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