Dilute solution viscometer

Measured in a Cannon-Ubbelohde semimicro dilute solution viscometer at 298.8 K. 

FIGURE 5.6 Dilute-solution viscometers (a) Ostwald (b) Ubbelohde. 

Figure 6S Dilute-solution viscometers a) Ostwald ( ) Ubbelohde.

Dilute Polymer Solutions. The measurement of dilute solution viscosities of polymers is widely used for polymer characterization. Very low concentrations reduce intermolecular interactions and allow measurement of polymer—solvent interactions. These measurements ate usually made in capillary viscometers, some of which have provisions for direct dilution of the polymer solution. The key viscosity parameter for polymer characterization is the limiting viscosity number or intrinsic viscosity, [Tj]. It is calculated by extrapolation of the viscosity number (reduced viscosity) or the logarithmic viscosity number (inherent viscosity) to zero concentration. 

In practice we do not measure viscosity directly. Instead, what is measured is time of flow for solutions and pure solvent in a capillary viscometer, the so-called efflux time. If the same average hydrostatic head is used in all cases, and since for very dilute solutions the density differences between the different concentrations are negligible, then the ratio of the efflux time of the solution, t, to that of the pure solvent, tg, may be taken as a measure of the ratio of the viscosities, i.e. 

Dilute Solution Viscometry - The hydrogenated and hydroformyl ated (10%) PBD were completely soluble in toluene. Intrinsic viscosity measurements were carried out in toluene at 30°C using a Cannon-Ubbelohde viscometer. 

The viscosities of products in solution (0.5 Weight %/volume) were measured by dilute solution viscometry using a Cannon Ubellohde viscometer at 35 °C. 

To perform this analysis, we first prepare a dilute solution of polymer with an accurately known concentration. We then inject an aliquot of this solution into a viscometer that is maintained at a precisely controlled temperature, typically well above room temperature. We calculate the solution s viscosity from the time that it takes a given volume of the solution to flow through a capillary. Replicate measurements are made for several different concentrations, from which the viscosity at infinite dilution is obtained by extrapolation. We calculate the viscosity average molecular weight from the Mark-Houwink-Sakurada equation (Eq. 5.5). 

V0 is the flow time through a viscometer of a reference liquid, and f is the flow time through the same viscometer of a dilute solution of polymer in the reference liquid. 

ISO 1628-4 1999 Plastics - Determination of the viscosity of polymers in dilute solution using capillary viscometers - Part 4 Polycarbonate (PC) moulding and extrusion materials ISO 7391-1 1996 Plastics - Polycarbonate (PC) moulding and extrusion materials - Part 1 Designation system and basis for specifications ISO 7391-2 1996 Plastics - Polycarbonate (PC) moulding and extrusion materials - Part 2 Preparation of test specimens and determination of properties ISO 11963 1995 Plastics - Polycarbonate sheets - Types, dimensions and characteristics. 

IL. Dilute solution viscosity measurements were done at 30 with the appropriate Ostwald-Fenske capillary viscometers. The water content of all organic solvents, used as the liquid phase in solid-liquid PTC runs was analyzed by potentiometric Karl Fischer titration using a Metrohm AG CH 9100 model automatic titrator. 

This unit describes a method for measuring the viscosity (r ) of Newtonian fluids. For a Newtonian fluid, viscosity is a constant at a given temperature and pressure, as defined in unit hi. i common liquids under ordinary circumstances behave in this way. Examples include pure fluids and solutions. Liquids which have suspended matter of sufficient size and concentration may deviate from Newtonian behavior. Examples of liquids exhibiting non-Newtonian behavior (unit hi. i) include polymer suspensions, emulsions, and fruit juices. Glass capillary viscometers are useful for the measurement of fluids, with the appropriate choice of capillary dimensions, for Newtonian fluids of viscosity up to 10 Pascals (Newtons m/sec 2) or 100 Poise (dynes cm/sec 2). Traditionally, these viscometers have been used in the oil industry. However, they have been adapted for use in the food industry and are commonly used for molecular weight prediction of food polymers in very dilute solutions (Daubert and Foegeding, 1998). There are three common types of capillary viscometers including Ubelohde, Ostwald, and Cannon-Fenske. These viscometers are often referred to as U-tube viscometers because they resemble the letter U (see Fig. HI.3.1). 

Physical Measurements. Intrinsic Viscosities. Intrinsic viscosities were obtained using dilute solution viscometry (Cannon-Ubbelohde viscometers). 

Physical Measurements. Molecular Weight. Intrinsic viscosities were determined using dilute solution viscometry (Cannon-Ubbelohde viscometers). For the poly (methyl methacrylate) polymer the following empirical expressions were used to obtain molecular weights (4) ... 

Since the density of a very dilute solution is approximately the same as the solvent itself, the relative viscosity (r r = r /r s) can be taken as the ratio of the time required for a given volume of fluid to flow through an Ubbelhode viscometer. The specific viscosity (r[sp) is then given by... 

Viscosity Measurements, Previous studies (2) have shown that dilute solutions of Pluronic F127 exhibit Newtonian flow characteristics and consequently, it is permissible that the viscosity of these solutions is measured by capillary viscometry. A suspended-level viscometer was used and solutions were thermostatted to within... 

The measurement of the size of the polymer is carried out in a capillary viscometer. The presence of polymer molecules in a solvent affects the relative motion of the solvent (i.e., solution viscosity). Even very dilute solutions of polymers are very viscous. When a dilute solution of a polymer travels along a capillary tube, as shown in Figure 7.5, there is a parabolic velocity gradient across the capillary tube with the maximum velocity at the center of the tube and a minimum velocity at the... 

Intrinsic Viscosity. Dilute-solution viscometry of samples in toluene was carried out in a Cannon-Ubbelohde semimicrodilution viscometer (size 25) in a temperature-controlled bath (25.0 0.2 °C). At least three concentrations were measured, and the results were extrapolated to infinite dilution by using the Huggins and Kramers relations... 

The densities of a dilute solution and solvent are usually assumed to be almost identical and as such this correction was thought to be negligible in an Ostwald or Ubbelohde viscometer. According to Eq. (44c) the relative viscosity is... 

As stated in Chapter 1, for the determination of intrinsic viscosity, [ ], of a polymer, viscosity values of several dilute solutions, when the relative viscosities ( / s) of the dispersions are from about 1.2 to 2.0, are determined. To facilitate such measurements, the so called Ubbelohde glass capillary viscometer is used that has a large reservoir to permit several successive dilutions of a polymer solution (Figure 3-19). Because intrinsic viscosity measurement is important, the test procedure for using the Ubbelohde viscometer is outlined here in brief (Cannon Instrument Co., 1982). 

A rheological instrument such as a viscometer can be used to evaluate t and 7 and hence obtain a value for the shear viscosity, 17. Examples of Newtonian fluids are pure gases, mixtures of gases, pure liquids of low molecular weight, dilute solutions, and dilute emulsions. In some instances, a fluid may be Newtonian at a certain shear-rate range but deviate from Newton s law of viscosity under either very low or very high shear rates (2). 

Measurement of viscosity [r ] is more complicated than estimation of the molar mass, due to the non-Newtonian behaviour of HA solutions during the flow. It is well known that the HA viscosity strongly depends on the shear rate (7) even for very dilute solutions. Unfortunately, the shear rate range of the usual viscometers used for the [rj] measurements, both off-line (i.e. Ubbelohde viscometer 1200-1500 s ) and on-line to a SEC system (i.e. DV 2500-3000 s ) are too high for measuring the HA... 

Dilute solution viscosities of most polymers were measured at room temperature in p-chlorophenol/1,2-dichloroethane (50/50 by weight), using an Ubbelhode viscometer. For samples containing HQ/RO, the viscosities were measured at 50°C in pentafluorophenol. In any case the molecular weight or viscosity of each sample was reported as nSR/c, or reduced viscosity, at 0.5 g/dl in the units of ol/g. 

Two replicates from each of the experimental treatments were evaluated for changes in viscosity. Dilute solutions (0.10, 0.20, 0.30, 0.40 and 0.50 g/lOOml) of nylon 6,6 dissolved in 90% formic acid were made. Viscosities of the dilute polymer solutions were determined at 25 + O.l C using a size 75 Cannon-Fenske capillary viscometer. Flow time measurements were repeated for each solution and for the pure solvent until three consecutive readings within 0.2 seconds or 0.1% of the mean were obtained (24). The average of the three consecutive flow times was used to determine the relative viscosity for each solution. 

The dilute solution viscosity measurements were conducted using Ubbelohde viscometers generally conducted at 25 + 0.05°C in a thermo-stated bath. The reduced viscosity or viscosity number [defined as (t -ri0)/ri0c, where 0 is the viscosity of the polymer solution, 0o is the viscosity of the solvent (or mixed solvent), and c is the concentration of polymer in g/100 mL] was calculated for each solution measured. 

Dilute Solution Viscosity Polymer dilute solution viscosity was measured at a concentration of 0.400g/dl of N,N-dimethyl-formamide[DMF, contained 0.05% n-propyliodide stabilizer16] at 25°C 0.1°C using an Ostwald-type viscometer. 

Capillary Viscometry. The viscosity of dilute solutions of the polymer was determined with a Canon-Fenske capillary viscometer set in a thermostat bath at 25 0.05 C. A stock solution of 0.15 g dL was prepared in distilled water, stored at 4 C for 2 days, and then filtered through a No. 1 sinter glass funnel to remove fibers and detritus from the preparation of the cellulose ether. Nine other solutions were prepared from this stock by dilution with filtered distilled water. All these solutions were then stored at 4 C for a further 24 h to ensure that all the solutions had the same temperature history, as this factor has been shown to be important in producing reproducible solutions of cellulose ethers (4, 5). The concentration range prepared was 0.015-0.15 g dL" and the flow times ranged from 294 to 1609 s. 

Dilute solution viscosities used for determining the intrinsic viscosity of the polymer systems in 2.0 wt % NaCl were obtained in a capillary viscometer (Ubbe-lohde) by using standard methods (iO, 11). Some of the measurements were obtained fi om an automatic capillary viscometer (Schott AVS/G). A conventional Huggins relationship 11) in which reduced viscosity is a linear function of polymer concentration was used to fit the data. A regression analysis was used to yield the intrinsic viscosity (the intercept) and the Huggins interaction coefficient, K, (the slope divided by the square of the intrinsic viscosity). 

It was assumed that the solutions were Newtonian at the shear rates in the capillary. This assumption was assessed with Couette viscometer measurements of these dilute solutions over a range of shear rates and was reasonable. Deviations were found for solutions at the higher concentrations, as indicated by negative departure from linearity of the reduced-viscosity-concentration plots these values were not used for intrinsic viscosity and Huggins constant determination. 

---