Absolute viscosity values

The differences in thickening properties are especially obvious when the viscosity of an emulsion concentrate with a defined particle size distribution is subsequently adjusted by means of a polymer or a lamellar fatty alcohol gel (Figure 12.2). Comparable absolute viscosity values are obtained after adding... 

In early hterature, the molecular weights of PVDC and VDC copolymers were characterized by the absolute viscosity of a 2 wt % solution in (9-dichlorobenzene at 140°C. The exact correlation between this viscosity value and molecular weight is not known. Gel-permeation chromatography is the... 

X = (lambda) yield factor, (W/W )with subscript o referring to reference value p = (mu) absolute viscosity at flowing temperature, centipoise (cp)... 

For Molecular weight determination by viscometry we do not need absolute h value, viscosity measurements may be carried out in simple Ostwald Viscometer. Because of (the non-Newtonian behaviour of most macromolecular solutions at high velocity gradients in the capillary, the viscometer dimensions are chosen in such a manner that the viscosity gradient is the smallest possible. 

Determine the kinematic viscosity of the oil Use Fig. 6.1 and Table 6.2 or the Hydraulic Institute—Pipe Friction Manual kinematic viscosity and Reynolds number chart to determine the kinematic viscosity of the liquid. Enter Table 6.2 at kerosene and find the coordinates as X = 10.2, Y = 16.9. Using these coordinates, enter Fig. 6.1 and find the absolute viscosity of kerosene at 65°F as 2.4 cP. Using the method of Example 6.2, the kinematic viscosity, in cSt, equals absolute viscosity, cP/specific gravity of the liquid = 2.4/0.813 = 2.95 cSt. This value agrees closely with that given in the Pipe Friction Manual. 

Since measured viscosities will vary depending on the dimensions of and the materials employed for the sample crucible and the rotating bob, measured values are related to absolute viscosities by means of an instrument factor. In these studies, the instrument factor was determined by tests with National Bureau of Standards glass viscosity standards whose viscosities are precisely defined and similar to those of the slags over the temperature range of interest. 

Viscosity measurements alone cannot be directly used in the Mark-Houwink-Sakurada equation to relate absolute viscosity and polymer molecular weight, since additional unknowns, K and a must be determined. Therefore, viscometry does not yield absolute molecular weight values it rather gives only a relative measure of polymer s molecular weight. Viscosity measurements based on the principle of mechanical shearing are also employed, most commonly with concentrated polymer solutions or undiluted polymer these methods, however, are more applicable to flow properties of polymers, not molecular weight determinations. 

The other alkali metals have been less extensively studied. The propagation rates of polystyrylsodium, -potassium, -rubidium and -cesium have been measured in benzene and cyclohexane [72, 73]. The sodium compound still shows half order kinetics in active centre concentration and is presumably associated to dimers. The rates for the rubidium and cesium compounds are directly proportional to the concentrations of the active chains which are presumably unassociated in solution. Absolute kp values can be determined from the propagation rate in this case. Poly-styrylpotassium shows intermediate behaviour (Fig. 11), the reaction order being close to unity at a concentration of the potassium compound near 5 x 10 M and close to one half at concentrations around 10" M. It could be shown by viscosity measurements that association was absent in the low concentration range. In this system both K2 and kp can be measured. The results are summarized in Table 2. The half order reactions show a large increase in kpK between lithium and potassium which... 

To measure the absolute viscosity eqn (3.9.2) must be solved, and so a value of y is needed. The discussion above indicates the conditions necessary to produce a constant wall correction, but there are unknowns, such as the sphere-to-wall separation, which make it impossible to calculate an actual theoretical value with sufficient accuracy. One must measure y empirically by observing the sphere velocity under conditions for which the fluid viscosity is known. For the rolling-ball viscometer, comparison is made with ambient-pressure viscosities whereas high-pressure data taken by the rolling-ball viscometer are used for comparison for the centrifugal-force viscometer. 

The time-temperature equivalence principle makes it possible to predict the viscoelastic properties of an amorphous polymer at one temperature from measurements made at other temperatures. The major effect of a temperature increase is to increase the rates of the various modes of retarded conformational elastic response, that is, to reduce the retarding viscosity values in the spring-dashpot model. This appears as a shift of the creep function along the log t scale to shorter times. A secondary effect of increasing temperature is to increase the elastic moduli slightly because an equilibrium conformational modulus tends to be proportional to the absolute temperature (13). 

Absolute viscosity, kg/m-s or Ib/ft-s (if, average value of liquid film ... 

The absolute viscosity of some common liquids at temperatures between -25 and 100°C is given in this table. Values were derived by fitting experimental data to suitable expressions for the temperature dependence. The substances are arranged by molecular formula in the modified Hill order (see Preface). All values are given in units of millipascal seconds (mPa s) this unit is identical to centipoise (cp). 

It can be proved that the refractive index of the mixtures depends linearly on the percentage of ethylene glycol. In the S-1 photoreaction both the photoisomerisation steps strongly depend on the absolute viscosity, whereas 3 is very small and stays nearly constant during the photoreaction. Since the determined values of quantum yield fit even for different mixtures of water/ethylene glycol with viscosity adjusted to the same value by variation of temperature (see Fig. 5.53), polarity effects of the solvent will influence the photoreaction less than viscosity effects [178]. 

By inserting the absolute values of R and N in equation (109) and by assuming a temperature of 300° absolute and an absolute viscosity of solvent of 0.01 (H2O at 20°) we obtain the very simple relation... 

The main attraction is that, because of the high surface area and aspect ratio, these benefits are potentially obtainable at much lower volume fractions than with most other established fillers. This has several potential advantages, notably lower cost, lower density, less opacity, and potentially less reduction in other properties such as impact strength. Because of viscosity effects associated with the plate shape and potential particle damage, and difficulties in obtaining and maintaining exfoliation, the practical loading level is, however, limited to about 10% which severely restricts the absolute property values achievable. These various aspects are discussed further next, with the emphasis on thermoplastic applications, which are currently of most interest. 

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