Ubbelohde-type capillary viscometer

To measure the flow time of a solution, the Ubbelohde-type capillary viscometer is used. The flow time of solution is compared with the flow time of base fluid (water). As an example. Figure 13.10 shows the relative viscosity for the PEO/SDS system. When surfactant is added to polymer solution, the hydrodynamic size of polymer is increased due to the attachment surfactant micelles to the backbone of PEO chains. This causes an increase in relative viscosity. The relative viscosity begins to rise at CAC as shown in Eigure 13.10.When the surfactant concentration reaches PSP, the relative viscosity begins to flatten. 

The Ubbelohde-type capillary viscometer gives viscosity at a low shear rate. To obtain the full viscosity-shear rate profile, a coaxial cylinder viscometer can be employed. The shear rate in a coaxial cylinder viscometer is calculated using the following equations ... 

Binding ratios of SDS (BHD Ltd.) and CPC (Tokyo Kasei Ltd.) to HPC (M.W. =11 -I5xl0 Tokyo Kasei Ltd.) were determined at 30 °C by an equilibrium dialysis method. Cloud point of an HPC solution was observed by the naked eye. Amounts of p-dimethylaminoazobenzene (Nakarai Ltd.) solubilized by the surfactant micelle and the surfactant-polymer complex were determined at 30 °C by colorimetry at 1 = 418 nm. Viscosity was measured by an Ubbelohde-type capillary viscometer, a cone-plate rotary viscometer, or a Brookfield-type rotary viscometer at 25 or 30 °C. Mean diameter of secondary particles of kaolinite in its dilute suspension (1 g/dl) was estimated by a Coulter counter (type TA-II) in 154 mmol/dm NaCl at room temperature. 

Figure 5.14 Typical suspension-type capillary viscometers, (a) Ostwald type (b) modified Ost-wald type (c) Ubbelohde type. From ref. 43, reprinted by permission of John Wiley Sons Inc.

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... 

Viscometric manipulations are simplified considerably by using the modified Ubbelohde viscometer described by Davis and Elliott.26,126 This type of capillary viscometer can be modified to enable an estimate of the shear correction to be made,127 although a Couette viscometer128 is more satisfactory for this purpose. 

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. 17.1 Two types of viscometers Ubbelohde (left) and Cannon-Fenske (right). The Ubbelodhe viscometer has the following components (1) fill tube, (2) capillary outlet, (3) pressure relief tube, (4) solution bulb, (5) suspended volume bulb, (6) lower flow bulb, (7) upper flow bulb, (8) upper timing mark, and (9) lower timing mark. The Cannon-Fenske Viscometer has the following components (1) fill tube, (2) capillary outlet tube, (3) solution bulb, (4) lower flow bulb, (5) upper flow bulb, (6) upper timing mark, and (7) lower timing mark.

The technique involving an evacuated capillary viscometer is limited to the measurement of polymer solutions having viscosities less than ca. 103 poise a point which has been made previously by Hadjichristidis and Roovers 132). This is a consequence of the viscometer type (Ubbelohde) which has been used in these determinations. Despite this practical limitation, it has been stated 78) that there is no inherent limit for viscosity measurements, even in conventional types of viscometers provided that the tubes are sufficiently wide. However, the limitations of operating with an evacuated viscometer, and the flow behavior of high viscosity (> 103 poise) polymer solutions, clearly reveals that the foregoing claim is unrelated to reality. 

The following viscometer has been found suitable Ubbelohde microviscometer (DIN SI 562, Part 2), capillary type Mil, viscometer constant about 0.1 mmJ/sJ. 

Capillary Viscometer An instrument used for the measurement of viscosity in which the rate of flow through a capillary under constant applied pressure difference is determined. This method is most suited to the determination of Newtonian viscosities. Various designs are used, such as the Ostwald and Ubbelohde types. 

In practical applications, flow of the material through an orifice is perhaps the most frequently encountered rheological phenomenon. It is then natural to be used for the viscosity measurement of suspensions (53-55). However, the flow through an orifice is not precise in terms of shear measurement because the shear rate is not well defined under such circumstances. To meet this objection, the orifice is in most cases extended to a tube. This leads to the capillary flow type of viscometers, the simplest, and for Newtonian fluids, the most accurate type, comprising the familiar Ostwald und Ubbelohde viscometers. The fully developed axial velocity in the laminar regime is given by... 

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. ... 

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 ... 

Dilute-solution viscosity (solution viscosity) n. (1) A catchall term that can mean any of the interrelated and quantitatively defined viscosity ratios of dilute polymer solutions or their absolute viscosities. (2) The kinematic viscosity of a solution as measured by timing the rate of efflux of a known volume of solution, by gravity flow, through a calibrated glass capillary that is immersed in a temperature-controlled bath. Two common types of viscometer are the Ostwald-Fenske and Ubbelohde. From the viscosities of the solution rj and the solvent 7o, and the solution concentration c, five frequently mentioned viscosities (viscosity ratios, actually) can be derived, as follows ... 

The kinematic and dynamic viscosities v and r), respectively, can be determined by a capillary viscometer of the Ubbelohde or Ostwald type (v = r]/Q). 

The most u,sed capillary viscometers are gravity-driven and correspond ib the Canon-Fenskc, Ostwald. and Ubbelohde types Fig. 19 shows a scheme of an Osiwatd capillary. In order to obtain viscosity, it is only necessary to measure the time / required for a given volume V of fluid to pass between the two marks. L, and L,. Thus, the Newtonian viscosity is... 

Viscosities for molecular weight determination are usually measured in glass capillary viscometers, in which the solution flows through a capillary under its own head. Two common types, the Ostwald and Ubbelohde, are sketched in Figure 5.6. (Since polymer solutions are non-Newtonian, intrinsic viscosity must be defined, strictly speaking, in terms of the zero-shear or lower-Newtonian viscosity (see Chapter 14). This is rarely a problem, because the low shear rates in the usual glassware viscometers give just that. Occasionally, however, extrapolation to zero-shear conditions is required.)... 

It is imperative to work with solutions of precisely known concentration and free of any dust. The solutions should not be too dilute (lack of precision) or too concentrated (interchain interactions). The ideal concentration range for viscosity measurements in a good solvent corresponds to 1.1 various types of capillary viscometers, with the Cannon-Ubbelohde viscometer being commonly used (Figure 6.16). Manual determination of the flow time (> 100 s) is sufficient for the viscosity measurements, but the greatest attention should be given to the temperature control. 

Earlier experiments involved the collection of SEC effluent aliquots to measure solution viscosity in batches with the very time consuming Ubbelohde drop-time type viscometers. A continuous capillary type viscometer was first proposed for SEC by Ouano. Basically, as shown in Figure 1, a single capillary tube with a differential pressure transducer was used to monitor the viscosity of SEC effluent at the exit of the SEC column. As liquid continuously flows through the capillary (but not through the pressure transducer), the detected pressure drop (AP) across the capillary provides the measure for the fluid viscosity (h) according to the Poiseuille s viscosity law ... 

The Ostwald and Ubbelohde viscometers, a series of glass bulbs which connected to a standard capillary, and the proportionality between t and r made relative measurements of viscosity under conditions of low shear rate fairly easy, particularly as thermostatting the whole device was simple (viscosity shows an Arrhenius-type temperature dependence, r = with typical E... 

Ubbelohde viscometer (1) (Cannon-Ubbelohde viscometer) An instrument made of Pyrex glass and consisting of an upper reservoir that drains through a marked capillary to a lower, vented chamber and thence to a second reservoir. The time taken by the test liquid to drain through the capillary is proportional to the viscosity (with slight corrections). This is one of several similar types used to measure viscosities of polymer solutions (see ASTM, www.astm.org). (2) Capillary... 

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