Viscosity measurements relative

Viscosity measures relative thickness or resistance of oil to flow. The viscosity of refined, bleached and deodorized (RBD) canola oil is higher than for soybean oil. Lang and co-workers (1992) and Noureddin and co-workers (1992b) found that the viscosity of canola and other vegetable oils was affected by temperature, similarly to other liquids. They derived an equation to calculate viscosity in the temperature range from 4-100°C. The viscosity of HEAR oil is significantly higher than that of canola oil. 

Strauss and Williamst have studied coil dimensions of derivatives of poly(4-vinylpyridine) by light-scattering and viscosity measurements. The derivatives studied were poly(pyridinium) ions quaternized y% with n-dodecyl groups and (1 - y)% with ethyl groups. Experimental coil dimensions extrapolated to 0 conditions and expressed relative to the length of a freely rotating repeat unit are presented here for the molecules in two different environments ... 

Once the value of the constant and the a value in Eq. (2.36) have been evaluated for a particular system, viscosity measurements constitute a relatively easy method for determining the molecular weight of a polymer. Criticize or defend the following proposition Since viscosity is so highly dependent on molecular weight for M > M, a 10% error in 17 will result in a 34% error in M above M, but only a 10% error in M below M, . 

Rheology. Flow properties of latices are important during processing and in many latex appHcations such as dipped goods, paint, inks (qv), and fabric coatings. For dilute, nonionic latices, the relative latex viscosity is a power—law expansion of the particle volume fraction. The terms in the expansion account for flow around the particles and particle—particle interactions. For ionic latices, electrostatic contributions to the flow around the diffuse double layer and enhanced particle—particle interactions must be considered (92). A relative viscosity relationship for concentrated latices was first presented in 1972 (93). A review of empirical relative viscosity models is available (92). In practice, latex viscosity measurements are carried out with rotational viscometers (see Rpleologicalmeasurement). 

Extrapolation to infinite dilution requites viscosity measurements at usually four or five concentrations. Eor relative (rel) measurements of rapid determination, a single-point equation may often be used. A useful expression is the following (eq. 9) (27) ... 

ASTM, Standard Test Method for Estimation of Molecular Weight (Relative Molecular Mass) of Petroleum Oils from Viscosity Measurements, ASTM Standard D-2502-92, 1992. 

This equation appears to have a number of names, of which the Mark-Houwink equation is the most widely used. In order to use it, the constants K and a must be known. They are independent of the value of M in most cases but they vary with solvent, polymer, and temperature of the system. They are also influenced by the detailed distribution of molecular masses, so that in principle the polydispersity of the unknown polymer should be the same as that of the specimens employed in the calibration step that was used to obtain the Mark-Houwink constants originally. In practice this point is rarely observed polydispersities are rarely evaluated for polymers assigned values of relative molar mass on the basis of viscosity measurements. Representative values of K and a are given in Table 6.4, from which it will be seen that values of K vary widely, while a usually falls in the range 0.6-0.8 in good solvents at the 0 temperature, a = 0.5. 

Most biological polymers, such as proteins and nucleic acids and some synthetic polymers, have relatively inflexible chains. For rigid particles, the size is no longer of predominant importance, because the polymer chain is no longer in the form of a flexible random coil instead, shape becomes an important parameter. Following are some theoretical proposals for the estimation of the shape factor p from the viscosity measurement (table 4). The term f/fo is sometimes denoted as p, Perrin constant. 

Viscosity measurements of the extracted polysaccharides cross-linked at increasing concentrations showed a clear increase in relative viscosity, when the cross-linking reaction took place at concentrations higher than 0.5 % (Fig. 4). At a concentration higher than 1.5 % a gel was formed. 

Viscosity Measurement. A Brookfield Viscometer (Model LVT, Brookfield Engineering Lab., Inc., Stoughton, Mass.) was employed for the measurement of relative viscosity. 

Table III. Measured Relative Molecular Weight, Passed Through GPC and Reduced Viscosities. Estimated Intrinsic Viscosities of Polymers Columns in Benzene ...

In polymer science we typically do not measure viscosity directly, but rather look at relative viscosity measures by determining the flow rate of one material relative to that of a second material. Viscosity is one of the most widely used methods for the characterization of polymer molecular weight because it provides the easiest and most rapid means of obtaining molecular weight-related data that requires minimal instrumentation. A most obvious characteristic of polymer solutions is their high viscosity, even when the amount of added polymer is small. This is because polymers reside in several flow planes (Figure 3.19b), acting to resist the flow of one plane relative to the flow of another plane. 

Cal ibr ation o f Instrument When 10 urn and 0.6 ym membranes were used to determine the viscosity of THF using the manufacturer s determination of M from the flow of water, the viscosities of THF were measured to be an average of 85 /, of the true value. The direct experimental P vs Q curves are shown in Figure 3. (There is, however, a systematic trend below 85 /. as membranes of even lower pore sues are used. Although this trend is puzzling it is unimportant for polymer research since most polymer solution studies need relative viscosity, specific viscosity,, measurements.)... 

The viscosity ratio or relative viscosity, T rel, is the ratio of the viscosity of the polymer solution to the viscosity of the pure solvent. In capillary viscometer measurements, the relative viscosity (dimensionless) is the ratio of the flow time for the solution t to the flow time for the solvent /fj (Table 2). The specific (sp) viscosity (dimensionless) is also defined in Table 2, as is the viscosity number or reduced (red) viscosity, which has the units of cubic meters per kilogram (m3/kg) or deciliters per gram (dL/g). The logarithmic viscosity number or inherent (inh) viscosity likewise has the units m3/kg or dL/g. For r red and rjmh, c, the concentration of polymer, is expressed in convenient units, traditionally g/100 cm3 but kg/m3 in SI units. The viscosity number and logarithmic viscosity number vary with concentration, but each can be extrapolated (Fig. 9) to zero concentration to give the limiting viscosity number (intrinsic viscosity) (Table 2). 

On the other hand, if the cure rate is much faster than the phase separation, then the morphology is controlled by the cure rate through a chemical pinning process. In this system, phase separation is mainly controlled by the cure rate of the epoxy matrix. Faster curing rates and shorter gel times lead to smaller PEI-rich particles with an increasing cure temperature. The temperature effect on the viscosity of reaction mixture is relatively small (i.e., the complex viscosities measured by Physica are 7 and 4 Pa.s at curing temperatures of 150 and 190°C, respectively). 

The simplicity of the Einstein equation makes it relatively easy to test, but also limits its usefulness rather sharply. With so few variables involved, the quantities we may evaluate by Equation (41) are few. Viscosity is a measurable quantity from which we try to extract information about the dispersion. All that Equation (41) offers directly in this area is the evaluation of 0 from viscosity measurements, again provided 0 is small and the particles are spheres. 

Variations in the temperature coefficient of viscosity with solvent, which have also been presented as evidence of association in concentrated solutions (135,143), could be similarly related to differences in Ta among the solutions. When free draining behavior is a possibility, the relative viscosities in different solvents should be compared at the same value of Co f°r the mixtures (that is, at constant free volume rather than at constant temperature). In any case, it is clear that a very well planned series of experiments is necessary in order to test for the existence of additional specific effects such as association. These comments are not meant to suggest that association can not occur at moderate concentrations. Indeed, the existence of association in various forms of polymethyl methacrylate seems well established (144). The purpose is rather to advocate that less specific causes be eliminated before association is inferred from viscosity measurements alone. 

Viscosity measures resistance to flow in a fluid. The units are kg m 1 s Relative to water, maple syrup is very viscous and hexane has low viscosity... 

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