Viscometry relative viscosity

Viscometry. Intrinsic viscosity. Kinematic viscosities (v=rj/p, where tj is the viscosity) were measured in a Cannon-Ubbelohde capillary viscometer. At least four concentrations, covering the relative viscosity range where the subscript s denotes the solvent) from about 1.8 to 1.2 were used to construct Schul -Blaschke plots. These plots of versus where... 

In polymer solution viscometry, it is not necessary to determine absolute values of the viscosity relative values are sufficient. These quantities are called viscosities, but the terms are misnomers because they are generally unitless ratios and therefore do not have the units of viscosity. In any case, the relative viscosity is simply the ratio of the... 

At the low polymer concentrations used in viscometry, Pps Psoiv therefore, from Equations 17.7-17.9, the relative viscosity becomes... 

Capillary viscometry is used for the determination of relative viscosity of polymer solutions in an appropriate solvent at diluted concentrations. Relative viscosity is dependent on concentration, so the concentration is specified for the solution. Relative viscosity is also dependent on the viscometer used therefore, the size of the tube used for the measurement... 

Viscometry is another simple technique that is used widely to detect possible interaction between polymer and surfactant. The relative viscosity (ijr) of a solution could be defined as the ratio of flow time of test solution (fp) to flow time of water (f J through the capillary of a viscometer ... 

Absolute measurements of viscosity are not required in dilute solution viscometry since it is only necessary to determine the viscosity of a polymer solution relative to that of the pure solvent. Application of Equation (3.166) leads to the following relation for the relative viscosity... 

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 opportunity to measure the dilute polymer solution viscosity in GPC came with the continuous capillary-type viscometers (single capillary or differential multicapillary detectors) coupled to the traditional chromatographic system before or after a concentration detector in series (see the entry Viscometric Detection in GPC-SEC). Because liquid continuously flows through the capillary tube, the detected pressure drop across the capillary provides the measure for the fluid viscosity according to the Poiseuille s equation for laminar flow of incompressible liquids [1], Most commercial on-line viscometers provide either relative or specific viscosities measured continuously across the entire polymer peak. These measurements produce a viscometry elution profile (chromatogram). Combined with a concentration-detector chromatogram (the concentration versus retention volume elution curve), this profile allows one to calculate the instantaneous intrinsic viscosity [17] of a polymer solution at each data point i (time slice) of a polymer distribution. Thus, if the differential refractometer is used as a concentration detector, then for each sample slice i. 

This was proven by measuring the HOCl/NaOCl consumption by different isolated monosaccharides [79,80]. As time-dependent data are obtained, the relative second order rate constants can be easily calculated. As resulted from one earlier study, viscometry in combination with gel chromatography was used to evaluate (a) the effects of the reagent HOCl and (b) effects of the complete myeloperoxidase (MPOl/HjOj/Ci system on HA solutions [81]. It was shown that even very small HOCl concentrations (in the pM range) led to a considerable reduction of the HA viscosity, whereas much higher concentrations of HOCl were required to induce the polymer fragmentation. This discrepancy was explained by structural changes in the HA polymer matrix that do already occur in the presence of very small amounts of HOCl [81]. 

In addition, there is a great utility of having reliable values for both Mark-Houwink and Schultz-Blaschke parameters in that the combination enables the measurement of an average molecular weight in a very simple viscometry experiment. Equation 10.17 gives an explicit formula for the intrinsic viscosity based only on the relative flow times for a single concentration experiment. 

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. 

One of the easiest means of determining the molar mass of a polymer is via viscometry. This yields the viscosity average molar mass, Mt . The viscosity of a polymer solution can be measured using capillary viscometers. The time for flow of the polymer solution through a given distance is measured and this is proportional to viscosity. The viscosity obtained by this method is expressed relative to that of the pure solvent. To determine molar mass, the intrinsic viscosity is required. It has this name because it relates to the intrinsic ability of a polymer to increase the viscosity of a solvent. The intrinsic viscosity [ j] is related to the specific viscosity jsp = 1 — rj/rjo, where rj is the viscosity of the polymer solution and rjo is that of the solvent via a virial equation in concentration resembling Eq. (2.9). It has been found empirically that for many polymer solutions the Mark-Houwink equation for intrinsic viscosity is obeyed ... 

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