Suspended level

The Ubbelohde viscometer is shown in Figure 24c. It is particularly useful for measurements at several different concentrations, as flow times are not a function of volume, and therefore dilutions can be made in the viscometer. Modifications include the Caimon-Ubbelohde, semimicro, and dilution viscometers. The Ubbelohde viscometer is also called a suspended-level viscometer because the Hquid emerging from the lower end of the capillary flows down only the walls of the reservoir directly below it. Therefore, the lower Hquid level always coincides with the lower end of the capillary, and the volume initially added to the instmment need not be precisely measured. This also eliminates the temperature correction for glass expansion necessary for Cannon-Fen ske viscometers. 

Figure 5 shows three different types of capillary viscometers often used for viscosity measurements of polymer solutions. The disadvantage of the Oswald viscometer is that the viscometer has to be charged with the solution to a precise level and fine adjustments need to be made at the temperature of measurement. The Ubbelohde viscometer, also frequently referred to as the suspended level viscometer, is particularly useful when a series of different polymer concentrations is to be measured. The filling volume needs not to be adjusted precisely. The largest dilution ratio obtainable is limited only by the ratio of the volume of bulb B to that of the volume between the bottom of bulb B and the top of bulb C. For the compact version (Figure 5(c)) smaller sample volume is needed. There are also capillary viscometers available that can be coupled with liquid... 

The Cannon-Fenske viscometer is used for measuring the kinematic viscosity of transparent Newtonian liquids, especially petroleum products and lubricants. The Ubbelohde viscometer is also used for the measurement of kinematic viscosity of transparent Newtonian liquids, but by the suspended level principle. 

In all cases, intrinsic viscosities were measured at 25 C in constant temperature baths controlled to +0.1°C or better, using suspended level Ubbelohde dilution viscometers with solvent flow times of at least 100 sec.. No kinetic energy corrections were made. Solution flow times were measured at four concentrations for each sample, and intrinsic viscosities were obtained from the classical double extrapolation of hg /c vs. c and (In hj.)/c vs. c to a single intercept value. Concentration ranges were varied somewhat with the molecular weights of the samples, but were chosen such that both functions were straight lines in all cases. 

When bulb D is partially full, unblock both tubes 1 and 3 and bulb B will drain, creating the suspended level at the bottom of the capillary in bulb B. 

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... 

Methods. Viscosity Measurements. Crosslinking reactions and reactions with butyl isocyanate were carried out in an Ubbelohde suspended-level viscometer modified to enable reactions to be carried out in an enclosed atmosphere. Viscometers were immersed in an oil bath at 80°C., and flow times were measured over periods of up to 10 days. Specific viscosities, 77, were then calculated. In general, runs were followed until the change in viscosity with time had become very small. Flow times were measured frequently enough to allow a smooth curve to be drawn when rj was plotted against reaction time a typical curve is... 

Solution Viscosity. The intrinsic viscosities [77] of the copolymers were measured for solutions in dry toluene at 25 °C. by dilution in an Ubbelohde suspended-level viscometer. Conventional plots of rj/c (18) and log (1 + r )/c (29) were found to be nonlinear for all copolymers where 77 is the specific viscosity. To get accurate values of the intrinsic viscosities and of the Huggins constants h and k2, triple plots were drawn as recommended by Heller (16). These gave the intercept 1/[iy], and fci and were determined directly from the initial slopes of the plots... 

Intrinsic viscosities of BBB in methanesulfonic acid were determined with a suspended level Ubbelohde viscometer by extrapolating the data for at least four concentrations to infinite dilution according to the simultaneous extrapolations ... 

Apparatus The Ubbelohde suspended level viscometer, shown in Fig. 5, is preferred to determine the viscosity of... 

FIGURE 12-25 Schematic diagrams of (a) an Oswald viscometer and (b) an Ubbelholde or suspended-level viscometer. 

UBBELOHDE VISCOMETER Fig.. 3-6. UbbelohJe suspended level viscometer. 

The requirement that the same amount of liquid should always be used does not apply in the case of the Ubbelohde suspended level viscometer [13], shown in Fig. 4.21(b). A modified design of the Ubbelohde viscometer is shown in Fig. 4.21(c). For measurement with the Ubbelohde viscometer a measured volume of polymer solution with known concentration is pipetted into bulb B through stem A. This solution is transformed into bulb C by applying a pressure on A with compressed air while column D is kept... 

Figure 4.21 Glass viscometers, (a) Ostwald viscometer (b) Ubbelhode suspended-level viscometer (c) A modified suspended-level viscometer (see text for description).

As mentioned earlier, viscometric manipulations are simplified considerably by using a capillary instrument of the Ubbelohde type, as modified by Davis and Elliott, rather than one of the Ostwald or Fenske t3q)e. This viscometer has a side arm at the base of the capillary which breaks the liquid flow to form a suspended level, and also reduces kinetic-energy corrections. The latter are very important, but can be made negligible by careful viscometer design. Kinetic-energy corrections are inversely proportional to the flow time, and so the viscometer should be designed so that solvent flow-times of 150-200 seconds are achieved. Full details of viscometric techniques can be found elsewhere. ... 

Since some of the solvents used on this study are mixed solvents, with both components having a high vapor pressure, it was necessary to study the viscosity of dilute solutions with sealed viscometers. Commercially available suspended level Cannon viscometers constructed to permit sealing under vacuum were used. The solution was filtered into the viscometer and degassed by successive freeze-thaw cycles, and the viscometer was sealed under vacuum. In use, the viscometer was mounted on a holder in a constant temperature bath to permit the rotation of the viscometer to the horizontal to fill the bulb, and rotation to the vertical for determination of the efflux time. 

One of the simplest methods of examining this effect is by capillary viscometry, although automatic viscometers are commercially available. In a U-tube viscometer such as the Ubbelohde suspended level dilution model shown in Figure 9.8, the flow times of pure solvent and a polymer solution t are recorded. This is done by pipetting an aliquot of solution of known volume into bulb D. The solution is then pumped into E. The flow time t is the time taken for the solution meniscus to pass from X to y in bulb E. 

Suspended-level Ubbelohde viscometers are so constructed that, during a measurement, the pressure head of the suspended liquid at the capillary outlet is independent of the amount of liquid originally introduced into the viscometer. This also means that solution originally introduced into the viscometer can be diluted with solvent to provide a series of concentrations without having, as in the case of the Ostwald viscometer, to empty and clean the viscometer after every measurement. On the other hand, the amount of liquid required for a measurement is higher in the Ubbelohde than in the Ostwad viscometer. Another advantage of the Ubbelohde suspended-level viscometer is that the stress on the suspended liquid exactly compensates the... 

RO reject (concentrate) contains nutrients and solids nitrate = 27 mg/1, phosphorous (as P) =7 mg/1, TDS = 6400 mg/1 and TSS = 30 mg/1. In order that the instantaneous nutrient and suspended solids loads in the receiving rivers do not exceed the stringent environmental limits, RO reject water undergoes biological treatment to achieve the following nutrient and suspended levels on a 50 percentile basis nitrate as N = 1 mg/1, phosphorous as P = 4 mg/1, and TSS = 10 mg/1. 

Figure 2.3 A suspended level viscometer (Ubbelohde) which readily allows for the dilution of a polymer solution in order to obtain the values of without cleaning the instrument between measurements with different concentration solutions.

Suspended-level Ubbelohde viscometers are so constructed that, during a measurement, the pressure head of the suspended liquid at the capillary outlet is independent of the amount of liquid originally introduced into the viscometer. This also means that solution originally introduced into the viscometer can be diluted with solvent to provide a series of con-... 

Viscosities were measured in capillary viscometers of the suspended level Ubbelohde type (Cannon Instrument Co.) using a Wescan Automatic Viscosity Timer. Corrections for kinetic energy effects were not necessary since flow times were well over 100 seconds in all cases. Viscosities at 25 C of at least four concentrations were measured and extrapolated to infinite dilution using the usual relations ... 

After closing the pressurization opening (left tube in Fig. 3.1b), the sample solution is to be carefully sucked in the middle tube via a water jet pump or an adequate device, until the meniscus clearly exceeds the v per mark Mj. Opening all three openings starts the experiment. This causes the liquid column to separate at the lower end of the capillary and to form a suspended level at the dome of the reservoir. The measurement is executed by measuring the time it takes for the meniscus of the solution to drop from the mark Mi to M2. 

Ubhelohde L (1937) The principle of the suspended level applications to the measurement of viscosity and other properties of liquids. Ind Eng Chem Anal Ed 9(2) 85-90... 

The above condition of always using the same volume of liquid does not apply, however, in the case of Ubbelohde suspended level viscometer (Ubbelohde, 1937), shown in Fig. 4.15(b). A modi ed design of the Ubbelohde viscometer is shown in Fig. 4.15(c). For measurement with the Ubbelohde viscometer a measured volume of polymer solution with known concentration is pipetted into bulb B through stem A. This solution is transferred into bulb C by applying a pressure on A with compressed air while column D is kept closed. When the pressure is released, the solution in bulb E and column D drains back into bulb B and the end of the capillary remains free of hquid. The solution ows from bulb C through the capillary and around the sides of the bulb E into bulb B. The volume of hquid in B has no effect on the rate of ow through the capillary because there is no back pressure on the liquid emerging from the capillary as the bulb E is open to atmosphere. The ow time t for the solution meniscus to pass between the ducial marks a and b... 

Various types are known such as Ostwald, Cannon-Fenske and Ubblehode (also referred to as a suspended level viscometer or SLV) as shown in Figure 3.2. 

Viscosity measurements are made either in a glass capillary such as a suspended-level viscometer or in a stainless steel differential viscometer. The measurement of the IV of a polyelectrolyte is hampered by intra- and inter-molecular ionic repulsion, and it is necessary to add buffers and electrolyte to the solution to suppress these forces. 

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