Effective viscosity measurement

The first viscosity measurements of nematic liquid crystals were performed with classical shear flow viscometers flow induces a change in orientation of the director, see EQN (4), so the effective viscosity measured is r o [54,55]. Since r o can be considered a relatively good approximation to the Miesowicz r i, conventional viscometers are still in use in conjunction with yi measurements [44,56,82,86]. However, for the purpose of measuring the viscosity anisotropy oldo instruments had to be modified and new ones developed. 

Effect of Temperature. In addition to being often dependent on parameters such as shear stress, shear rate, and time, viscosity is highly sensitive to changes in temperature. Most materials decrease in viscosity as temperature increases. The dependence is logarithmic and can be substantial, up to 10% change/°C. This has important implications for processing and handling of materials and for viscosity measurement. 

Viscoelastic Measurement. A number of methods measure the various quantities that describe viscoelastic behavior. Some requite expensive commercial rheometers, others depend on custom-made research instmments, and a few requite only simple devices. Even quaHtative observations can be useful in the case of polymer melts, paints, and resins, where elasticity may indicate an inferior batch or unusable formulation. Eor example, the extmsion sweU of a material from a syringe can be observed with a microscope. The Weissenberg effect is seen in the separation of a cone and plate during viscosity measurements or the climbing of a resin up the stirrer shaft during polymerization or mixing. 

Measurements of the effective viscosity as a function of composition may be fitted to equation 80 or presented in graphic form as in Figure 16. The correction factor, R, also may be determined by accounting for the volume fraction, ti , of particles through the Andress formula ... 

SFA has made a great contribution to the investigations of thin him rheology [41], The measurements on SFA conhrm that there is a signihcant enhancement of the effective viscosity in molecularly thin liquid hlms, and the viscosity grows constantly as the him thickness diminishes. 

Fig. 7—Viscosity enhancement of confined iiquid (a) effective viscosity of dodecane measured on SFA [18] (b) effective viscosity of hexadecane measured on interferometer [19],...

Fig. 8—Effective viscosity of confined hexadecane measured on SFA as a function of shear rate and film thickness, from which it is seen that the shear thinning gradually disappears as the film thickness increases and the viscosity finally has approached the bulk values at h=122 nm.

A final comment has to do with the concept of effective viscosity In strongly Inhomogeneous fluids. For these systems the definition of the effective viscosity depends on the type flow, hence different effective viscosities will be measured for different flow situations In the same system with the same density profile. Therefore, the effective viscosity Is a concept of limited value and measurements of this quantity do not provide much information about the effects of density structure on the flow behavior. 

Diffusion and sedimentation measurements on dilute solutions of flexible chain molecules could be used to determine the molecular extension or the expansion factor a. However, the same information may be obtained with greater precision and with far less labor from viscosity measurements alone. For anisometric particles such as are common among proteins, on the other hand, sedimentation velocity measurements used in conjunction with the intrinsic viscosity may yield important information on the effective particle size and shape. ... 

Intrinsic viscosity measurements were done with a large number of solvents varying in pH, ionic strength, etc., using Cannon-Ubbelohde semimicro dilution viscometers. This was done to provide information on the effect of mobile phase composition on the size of a polymer molecule in solution and thus to facilitate the interpretation of GPC behavior. 

Water content and viscosity measurements in certain systems show a correlation to emulsion stability [597]. The viscosity provides a more reliable measure of emulsion stability, but measurements of the water content are more convenient. Mixing time, agent amount, settling time, and mixing energy impact the effectiveness of an emulsifier. 

The viscosities were measured with an Ubbelohde Cannon 75-L, 655 viscometer. Formic acid was chosen as the solvent for the viscosity measurement because the polymer (VII) showed very low or no solubility in other common solvents. In a salt free solution, a plot of the reduced viscosity against the concentration of the polymer showed polyelectrolytic behavior, that is, the reduced viscosity ri sp/c increased with dilution (Figure 4). This plot passed through a maximum at 0.25 g/dL indicating that the expansion of the polyions reached an upper limit, and the effects observed on further dilution merely reflected the decreasing interference between the expanded polyions. 

The results show that although all the demulsifiers lower the shear viscosity, they differ widely in their demulsification effectiveness, as measured by the residual bottom sediment and water content (Figure 1) (BS and W%) of the dehydrated oil. For example, the demulsifier 0P1, although it lowers both the equilibrium interfacial tension (Figure 2) and the shear viscosity (Table I), nevertheless is ineffective. This is because it takes a much longer time for the oil-water interfacial tension to reach equilibrium with 0P1 than with PI or P2 (see later). 

Second, due to the difficulty of accessing multiphase flows with laser-based flow diagnostics, there is very little experimental data available for validating multiphase turbulence models to the same degree as done in single-phase turbulent flows. For example, thanks to detailed experimental measurements of turbulence statistics, there are many cases for which the single-phase k- model is known to yield poor predictions. Nevertheless, in many CFD codes a multiphase k-e model is used to supply multiphase turbulence statistics that cannot be measured experimentally. Thus, even if a particular multiphase turbulent flow could be adequately described using an effective viscosity, in most cases it is impossible to know whether the multiphase turbulence model predicts reasonable values for... 

Because solvent viscosity experiments indicated that the rate-determining step in the PLCBc reaction was likely to be a chemical one, deuterium isotope effects were measured to probe whether proton transfer might be occurring in this step. Toward this end, the kinetic parameters for the PLCBc catalyzed hydrolysis of the soluble substrate C6PC were determined in D20, and a normal primary deuterium isotope effect of 1.9 on kcat/Km was observed for the reaction [34]. A primary isotope effect of magnitude of 1.9 is commonly seen in enzymatic reactions in which proton transfer is rate-limiting, although effects of up to 4.0 have been recorded [107-110]. 

There is little new information available on the heat inactivation of fungal PG. Weitnauer,48 using a questionable technique47 of viscosity measurements and entirely disregarding the possible effect of PM, found that the PG solutions were inactivated by holding for a few hours at 40° and that there is a noticeable drop in activity even at 30°. This is in good harmony with the common experience that the PG activity in solu-... 

Fig. 34 Effect of the dispersion temperature and the degree of dispersion of P.Y.13 on the viscosity and CPVC of sheet offset inks. Viscosity measurement at 23° C.

The rotation of a paddle in a fluidised bed provides a means of measuring an effective viscosity of the bed in terms of the torque required to rotate the paddle at a controlled speed(53). 

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