Viscometry shear rate

Figure 5,16. It is assumed that by using an exactly symmetric cone a shear rate distribution, which is very nearly uniform, within the equilibrium (i.e. steady state) flow held can be generated (Tanner, 1985). Therefore in this type of viscometry the applied torque required for the steady rotation of the cone is related to the uniform shearing stress on its surface by a simplihed theoretical equation given as...

In order to understand polymer solution behaviour, the samples have to be characterised with respect to their molecular configuration, their molar mass and polydispersity, the polymer concentration and the shear rate. Classical techniques of polymer characterisation (light scattering, viscometry, ultracentrifugation, etc.) yield information on the solution structure and conformation of single macromolecules, as well as on the thermodynamic interactions with the solvent. In technical concentrations the behaviour of the dissolved polymer is more complicated because additional intramolecular and intermolecular interactions between polymer segments appear. 

The concentration at which a steep rise in this curve begins has been termed as the critical or threshold concentration (2,3). Figure 6 shows such typical curves for PTF and BTF in n-hexane. Despite the fact that different shear rates are involved in capillary viscometry, it can be qualitatively said that at a given concentration, PTF viscosified n-hexane better than BTF. It is clear from Figure 6 that the critical concentration for these two compounds is above 0.7%, while analogous tri-n-alkyltin fluorides showed a critical concentration of less than 0.4% (3). This may be due to the presence of bulky Me3Si-groups nearer to the Sn-F bond, which causes some steric hindrance to auto-association. 

Define rheology, shear force, shear stress, shear rate, Newtonian fluid, dynamic viscosity, centi-poise, kinematic viscosity, centistokes, viscometry, and viscometer. 

Measurements of the zero shear viscosity (20 °C) were made with a Bohlin VOR rheometer in the viscometry mode. If a Newtonian region was not found at the lowest measurable shear rates, the samples were characterized with a Bohlin-CS constant stress rheometer, with which it was possible to obtain extremely low shear rates. This approach was especially needed for highly viscous samples exhibiting pseudoplastic behavior on the VOR rheometer. Newtonian regions were found for each sample in this manner, yielding the zero shear viscosities reported. 

A study, relevant to recirculation behaviour in a RRIM machine, of polyol and polyol slurry rheology at shear rates in the range 0-103 s 1. This study is based on viscometry with modified cone and plate geometry. 

High shear rate viscometry, extending to 10 s"1, simulating conditions in the mixing head, using a capillary viscometer attached to a RRIM machine. 

Gustafsson, J., Nordenswan, E., and Rosenholm, J.B., Shear-induced aggregation of anatase dispersion investigated by oscillation and low shear rate viscometry, 7. Colloid Interf. Sci., 242, 82, 2001. 

A rotating body immersed in a liquid experiences a viscous drag or retarding force, and this principle can be applied to viscometry. The chief advantage of rotational viscometry is that continuous measurements at a given shear stress or rate of shear can be made over extended periods of time. Thus time-dependent changes in flow properties can be measured conveniently. Another advantage of rotational viscometry is the ease with which shear rate can be altered. 

Figure 8.4 Determination of shear rate (kj from experimental data, (a) Non-Newtonian power consumption (b) Newtonian power consumption (c) non-Newtonian viscometry...

There are many relative viscometric methods, i.e., those which require calibration with a fluid of known viscosity. Although they may be useful for viscometry of Newtonian fluids and for process and product control, the relative methods are inappropriate for adhesive materials, since concentrated colloidal dispersions and concentrated solutions of macromolecules show non-Newtonian behavior. While macromolecular systems usually exhibit viscoelasticity, colloidal dispersions can often be considered to be purely viscous. Non-Newtonian behavior can be characterized in steady shear, and is usually expressed as the functional dependence of shear stress on shear rate, or of viscosity on shear rate. 

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