Viscometer, capillary Ostwald

The oxidative degradation of polyfvinyl alcohol) is followed at 25 °C by viscosity measurements in an Ostwald viscometer (capillary diameter 0.4 mm). One proceeds as follows ... 

Ostwald viscometer (capillary diameter, 0.5 mm e.g., Fisher Scientific) Constant-temperature mechanism (e.g., appropriate water bath)... 

About 20 ml of the poly(amide acid) solution are then dropped into 300 ml of water with vigorous stirring. The precipitated colorless polymer is filtered with suction, washed several times with water, and dried in vacuum at lOO C for 20 min. The limiting viscosity number is determined in dimethylformamide at 25°C (Ostwald viscometer, capillary diameter 0.4 mm). 

The basic design is that of the Ostwald viscometer a U-tube with two reservoir bulbs separated by a capillary, as shown in Figure 24a. The Hquid is added to the viscometer, pulled into the upper reservoir by suction, and then allowed to drain by gravity back into the lower reservoir. The time that it takes for the Hquid to pass between two etched marks, one above and one below the upper reservoir, is a measure of the viscosity. In U-tube viscometers, the effective pressure head and therefore the flow time depend on the volume of Hquid in the instmment. Hence, the conditions must be the same for each measurement. 

Fig. 24. (a) Ostwald glass capillary viscometer, (b) Cannon-Fenske viscometer, and (c) Ubbelohde viscometer. 

The original Ostwald viscometer has been modified in many ways, and a number of different versions are on the market (Table 4) (21). Most are available with a wide choice of capillary diameters and therefore a number of viscosity ranges. A number of viscometers are described in ASTM D445, which also Hsts detailed recommendations on dimensions and methods of use. 

Osteoporosis biomarkers, 17 649 Ostromislensky, Ivan, 25 628 Ostwald color system, 7 309 Ostwald glass capillary viscometer, 21 728 Ostwald ripening, 10 124... 

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. 

Capillary viscometers that have this design are called Ostwald viscometers. There are many specific designs of Ostwald viscometers. The most frequently used are the Cannon-Fenske viscometer... 

The Ostwald viscometer is the general name given to a capillary viscometer. 

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. 

An Ostwald viscometer is similar to an Ubbelohde-type rheometer except that it is simpler in design and is less expensive. A schematic of an Ostwald viscometer is shown in Fig 3.6(b). It is characterized by a lower bulb that acts as a solution reservoir. A solution of known polymer concentration is placed in the lower bulb. A single capillary tube in which the measurement is taken is connected to the bottom of the bulb and to two small bulbs at the top of the capillary. Fluid is forced from the lower bulb through the capillary into the two small bulbs attached to the top of the capillary. There is a line between the two bulbs and at the exit of the lower bulb. The fluid is then allowed to drain back into the lower bulb through the capillary, and the time for the fluid to travel between the two lines is recorded. The time, if there were no end effects, is proportional to the kinematic viscosity (/j/p). 

Figure 3.6 Solution capillary rheometers a) Ubbelohde-type rheometer (courtesy of Cannon Instrument Company, USA), and b) a schematic of an Ostwald viscometer...

Fig. 2.15a. Ostwald viscometer Total length 25 cm capillary length 10 cm bulb 3 diameter 1.3 cm, bulb 4 diameter 2.2 cm, filling level 2 or 3 ml, flow volume 0.5 ml a, b head pieces c sintered glass filter for filtration of solvent and polymer solution...

With the viscosity of a liquid we mean the resistance to flow of that particular liquid. This resistance is caused by internal friction and other interactions between the particles. Among other things, viscosity is dependent on temperature, the solid volume fraction and the properties of the particles. The viscosity of normal liquids, solutions and lyophobic colloids which are not too concentrated and contain symmetrical particles is measured by allowing a certain volume to flow through a capillary and measuring the time required by the liquid to flow through it. In figure 5.10 you can see the instrument which is used for this measurement the Ostwald viscometer. 

The capillary method is simple to operate and precise (c. 0.01-0.1 per cent) in its results, but suffers from the disadvantage that the rate of shear varies from zero at the centre of the capillary to a maximum (which decreases throughout the determination) at the wall. Thus, with asymmetric particles a viscosity determination in an Ostwald viscometer could cover various states of orientation and the measured viscosity, although reproducible, would have little theoretical significance. 

The Ostwald Viscometer Method There are a number of methods of different kinds of measuring viscosity. The method commonly employed is the Ostwald s viscometer method which is based on Poiseullie s law. This connects the rate of flow of a liquid through a capillary tube with the coefficient of viscosity of the liquid and is expressed by the equation... 

Viscosity. The viscosity of ozone-fluorine mixtures was determined in a modified Ostwald viscometer (1) which was used with a variable volume of liquid. The viscometer was made from precision-bore glass tubing (4 mm. i.d.) with a capillary section 0.203 mm. in diameter and 12 on. long. 

Many types of apparatus used by earlier investigators as vis-cometerss are only of historical interest. A handy simple apparatus which is often used in laboratories (although it has some defects) is that known as tht Ostwald viscometer (Fig. l.VIII E). The time taken for the level to fall from a to 6 by way of the capillary be is found, the liquid being first sucked from the bulb A above the mark a by a piece of rubber tubing attached to B. The apparatus must be enclosed in some type of constant temperature bath Ostwald used an inverted bell-jar filled with water... 

The pressure gradient along the capillary of an Ostwald viscometer is given by the Hagen-Poiseuille law ... 

Viscosity Measurements. Viscosities were determined using an Ostwald-Fenske capillary viscometer. Measurements were made at 25°C and at a concentration or 2.5 mg/mL in 1 1 phenol-chlorobenzene. 

As an example of a simple modern capillary viscometer let us examine the Cannon-Fenske modification of the Ostwald viscometer, illustrated in Fig. 4-6. A specified volume of liquid is charged into the viscometer in the bottom reservoir A, and the liquid is then carefully drawn up through the capillary into the bulb B. The volume between the markers I and II is known precisely. The upper bulb T serves as a reservoir for the amount of liquid required to get the viscometer into steady-state operation. 

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