Centrifugation viscometers

The desired amount of this collagen solution was diluted (0.2 ml to 10 ml) with citrate buffer, pH 4.0 and then dialyzed overnight against the buffer to be used. 2 ml of that solution were then diluted to 10 ml with the appropriate buffer, centrifuged in the cold (40000 g for one hour) and the supernatant immediately decanted into the viscometer in the cold room (10°C)... 

Freshly collected venous blood is anticoagulated with 1 mg/ml blood K+-EDTA or heparin sodium (5 IU/ml blood) and centrifuged at 3000 rpm for 5 min. The supernatant (plasma) is removed and a sample of 0.9 ml plasma is transferred into a capillary viscometer... 

Viscosity Transfer an accurately weighed sample, equivalent to 5.0 g on the dried basis, into a 250-mL beaker. Adjust the rotor of a variable-speed stirrer about 1 in. above the sample, add 195 mL of recently boiled and cooled water, and stir at a speed that will avoid undue aeration. Continue stirring for about 1.5 h, then either set aside for 3 h or overnight, or centrifuge to expel any entrapped air. Adjust the temperature to 20° 0.1°, and determine as directed under Viscosity of Methylcellulose, Appendix IIB, using a Viscometer for High Viscosity. 

Straight-tube absolute viscometer was used by Gurney and by Walker. Lidstone used a vertical capillary with mercury below, which on running out drew in a liquid from a cup at the top. A horizontal viscometer using centrifugal force was suggested by Cope. An apparatus with a constant-temperature vapour jacket was used by Baume and Vigneron. ... 

To measure the absolute viscosity eqn (3.9.2) must be solved, and so a value of y is needed. The discussion above indicates the conditions necessary to produce a constant wall correction, but there are unknowns, such as the sphere-to-wall separation, which make it impossible to calculate an actual theoretical value with sufficient accuracy. One must measure y empirically by observing the sphere velocity under conditions for which the fluid viscosity is known. For the rolling-ball viscometer, comparison is made with ambient-pressure viscosities whereas high-pressure data taken by the rolling-ball viscometer are used for comparison for the centrifugal-force viscometer. 

Two representative fluids, methanol and 1,2-propanediol, are described here to illustrate the capabilities of rolling-ball and centrifugal-force viscometers. Both our samples were from Aldrich (with stated purity of greater than 99 per cent). The methanol was dried over a molecular sieve to remove water. Each fluid was loaded with a ruby chip and a metal sphere into a diamond cell. For methanol, a high tilt angle (65°) was necessary because of... 

Fig. 3.51 The high-pressure viscosity of ( , o) methanol and ( , ) 1,2-propanediol. The filled data points were obtained with a rolling-ball viscometer and the open data points were obtained with a centrifugal-force viscometer, the curves are a free-volume fit (Fig. 3.53). Methanol data, for pressures up to 3 GPa obtained by (x) Bridgman and (-I-) Herbst eta/. are in excellent agreement with our results. Crystallization of the methanol sample limited measurements to 8.3 GPa while the maximum viscosity for 1,2-propanediol limited the experimental pressure to 2.9 GPa.

Fig. 3.52 A centrifugal-force viscometer. The —50 xm diameter nickel ball is driven along the horizontal diamond surface by centrifugal force. The rotation of a mirror on the shaft of the rotor deflects a laser beam across a detector to produce a signal whose frequency gives the speed of the rotor. Our current centrifuge is able to generate an acceleration of 17000 m s (Reprinted with permission from J. Phys. Chem. 1993, 97, 2355. Copyright 1993. American Chemical Society.

Measuring viscosity with the centrifugal-force DAC viscometer... 

This procedure describes the use of DAC centrifugal-force viscometers which are useful in the range 10 s 10 Pa s. Viscosities from DAC rolling-ball viscometers (see Protocol 2) are used here to convert the measured relative viscosities into absolute values. Loading of the DAC with a ruby manometer chip, a nickel sphere, and the experimental fluid is described in Protocol 1. 

KEYWORDS asphalt, binder, asphalt-aggregate interaction, adhesion, chromatography, centrifugation, sliding plate viscometer, differential scanning calorimetry, atomic force microscopy... 

Cook, R.L., Herbst, C.A. King, Jr., H.E. (1993). High- iessuie viscosity of glass-forming liquids measured by the centrifugal force diamond anvil viscometer. J. Phys. Chem., 97, 2355-2361. 

Cone-and-plate viscometers of the type shown here are usually limited to fairly low shear rates. At higher shear rates, solutions tend to be flung from the gap by centrifugal force, and melts tend to ball up (like rubbing a finger over dry mbber cement). These problems can be overcome by enclosing the fluid around a biconical rotor, giving, in effect, two cone-and-plate viscometers back-to-back [6]. The flow curves earlier in this chapter were obtained with such a device. 

---