Dynamic viscosity experimental data

Although the theory of polyelectrolyte dynamics reviewed here provides approximate crossover formulas for the experimentally measured diffusion coefficients, electrophoretic mobility, and viscosity, the validity of the formulas remains to be established. In spite of the success of one unifying conceptual framework to provide valid asymptotic results, in qualitative agreement with experimental facts, it is desirable to establish quantitative validity. This requires (a) gathering of experimental data on well-characterized polyelectrolyte solutions and (b) obtaining the relationships between the various transport coefficients. Such data are not currently available, and experiments of this type are out of fashion. In addition to these experimental challenges, there are many theoretical issues that need further elaboration. A few of these are the following ... 

The derivation of fundamental linear viscoelastic properties from experimental data obtained in static and dynamic tests, and the relationships between these properties, are described by Barnes etal. (1989), Gunasekaran and Ak (2002) and Rao (1992). In the linear viscoelastic region, the moduli and viscosity coefficients from creep, stress relaxation and dynamic tests are interconvertible mathematically, and independent of the imposed stress or strain (Harnett, 1989). 

A study of the flow of a polyhedral foam in a regime of slip at the tube walls has been conducted [39]. It has been established that the rise in the dynamic viscosity of the foaming solution leads to diminishing the flow rate but to a much lesser extent at t0 = 1.25 Pa. Thus, a two fold increase in viscosity causes a 1.3 times decrease in the flow rate, while a 6 times increase in the dynamic viscosity only a 2.23 times decrease. This is probably related to the expanding of the effective thickness of the liquid layer 8 (ca. 3 times). The transition from plug flow (slip regime) to shear flow occurs at To = 9-10 Pa. This value of the shear stress is much smaller than the one obtained from Princen s formula for a two-dimensional foam (Eq. (8.18)) at a given expansion ratio and correlates well with To calculated from Eq. (8.24) and the experimental data of Thondavald and Lemlich [23],... 

These laws are in very good qualitative agreement with the large number of available experimental data on the dynamic behaviour of linear flexible entangled polymers, but quantitative departures still remain between the experiments and the predictions, as for example the fact that the exponent of the power law which characterises the variation of the zero shear viscosity with the molecular weight is observed to be 3.3 or 3.4 [3, 6] rather than the predicted value 3. These deviations have lead to a long controversy on the validity of the reptation model, and have stimulated a series of experimental and theoretical investigations to try to understand the limitations of this model and to propose the necessary modifications to obtain a better description of the dynamic properties of liquid polymers [7 to 22]. 

The excluded-volume parameter for PS was derived from viscosimetric data in good solvent collected by Nystrom and Roots for different molecular masses [113], The internal viscosity characteristic time Tq was obtained from best-fit data [12] of mechanical-dynamical results due to Massa, Schrag, Ferry, and Osaki [102,103] (see Figure 10). In analogy with what was previously found by other authors, notably Kirkwood and Riseman on the same polymer (PS) with different solvents [19], fitting the experimental data seems to require two different values of R ff = C/6to/s, one to obtain v q) through Eqn. (3.1.9) and a second one to evaluate to = I kg T, the latter... 

Using these empirical equations in conjunction with the predictions of the Bird-Carreau model, it is possible to predict t/ and An example of such a plot is shown in Fig. 24 for a 1.0% CMCguar blend (3 1). Experimental data are superimposed on these plots to judge the aptness of the model. The steady shear viscosity 17 and the dynamic viscosity 17 are well predicted in the shear rate range of 0.1 to 100 sec . The experimental data, as well as the theoretical prediction, portray commonly observed behaviors by polymeric dispersions. In this instance, 17 and rf for this blend ratio tend to some value, a property suggested by the Bird-Carreau model at low shear rate (Kokini et al, 1984). 

Murch [185] succeeded in establishing the influence of certain 2Jhysical proi)erties of the mixture on the separating effect. He found that the height of a separating stage is directly proportional to the expression r)jQ, in which is the relative volatility, 1/ the dynamic viscosity in centipoises and q the density in g/ml. By an evaluation of experimental data Murch arrived at the following empirical formula ... 

The cone and plate viscometer gives reliable experimental data over an extensive range of shear rates (10 -10 sec ). Not only can it be used to measure viscosities in simple shear, but it can also be used to determine the dynamic properties of viscoelastic materials. The unit is also set up to measure the normal stresses exhibited by viscoelastics, i.e., those perpendicular to the plane of shear. 

An analysis which has been done and also the generalization of obtained experimental data show, that as same as in a case of the low-molecular liquids, an investigation of the viscosity of polymeric solutions permits sufficiently accurately to estimate the characteristic time of the segmental motion on the basis of which the diffusion coefficients of the polymeric chains in solutions and melt can be calculated in other words, to determine their dynamical characteristics. 

In the fluid dynamic design with Models 1-3, information on the density and viscosity of the mixtures is needed, which usually has to be estimated as no experimental data is available. This can, however, be done with an accuracy sufficient for most cases using standard methods [8]. 

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