Viscometer, Brookfield calibration

Characterization. Absolute viscosities of the diols were measured with a Brookfield viscometer (model RVTD, spindle no. 4). The viscometer was calibrated with silicone oil viscosity standards supplied by Brookfield Engineering Laboratories, Inc. The diol was contained in a test tube, I.D.= 7.25 mm, and temperature control was achieved through a water bath. 

Other Rotational Viscometers. Some rotational viscometers employ a disk as the inner member or bob, eg, the Brookfield and Mooney viscometers others use paddles (a geometry of the Stormer). These nonstandard geometries are difficult to analyze, particularly for an infinite bath, as is usually employed with the Brookfield and the Stormer. The Brookfield disk has been analyzed for Newtonian and non-Newtonian fluids and shear rate corrections have been developed (22). Other nonstandard geometries are best handled by determining instrument constants by calibration with standard fluids. 

Procedure Using a suitably calibrated atomic absorption spectrophotometer and following the manufacturer s instructions for optimum operation of the spectrophotometer, determine the absorbance of the Standard Solution and of the Sample Solution at 589.0 nm. The absorbance of the Sample Solution is not greater than that of the Standard Solution. Viscosity of a 50% Solution Dissolve 200 g of sample, calculated on the dried basis and accurately weighed, in 200 mL of water contained in a 500-mL beaker. Equilibrate the solution at 25°, and measure its viscosity with a Brookfield viscometer A (model LVG, or equivalent), using a number 2 spindle at 20 rpm. 

Equipment. A Brookfield synchro-lectric viscometer, serial no. 758, is used to measure viscosity in the range of 0-100,000 cP. Sugden s double capillary modification of the maximum bubble pressure method is used to determine surface tensions. The apparatus is calibrated with benzene and is checked by determining the surface tension of chloroform at 25°C, which is found to be 23.5 dyn cm"1 (26.5 dyn cm 1) (35). 

A Brookfield viscometer with a helipath attachment (Stoughton, MA) is a useful rheological instrument for measuring the settling behavior and structure of pharmaceutical suspensions and for characterizing the properties and stability of flocculated suspensions. The viscometer should be properly calibrated to measure the apparent viscosity of the suspension at equilibrium at a given temperature to establish suspension reproducibility. Apparent viscosity, like pH, is an exponential term, and therefore the log-apparent viscosity is an appropriate way of reporting the results. 

Rotational viscometer n. An instrument for measuring the viscosity of pourable liquids, slurries, plastisols, and solutions. Most are of the bob-and-cup type. In these, the bob is a polished, accurate cylinder that is immersed in the liquid contained in the cup. Either the bob or cup is rotated and the torque on one or the other is measured, as is the rotational velocity. From these and the dimensions, the viscosity can be inferred, either directly by calculation from principles or indirectly by calibration with standards of known viscosity. An instrument widely used in the plastics industry is the Brookfield viscometer. 

Where viscometers are available the viscosity should be recorded. Viscometers such as the Brookfield LVT are recommended. Flow cups may also be used although they are difficult to calibrate. Bubble tubes such as Gardiner Tubes can be used for clear products. 

Viscosities were measured at a shear rate of 12 rpm (14.7 sec M using a calibrated Brookfield LVT viscometer equipped with a UL adapter. Screen-... 

The cone and plate viscometer is ideal for determining the absolute viscosity of fluids in a small sample volume. The commercially available cone and plate viscometer (e.g., Wells-Brookfield), a precise torque-measuring system, which consists of a calibrated beryllium-copper spring connecting the drive mechanism to a rotating cone, senses the resistance to rotation caused by the presence of sample fluid between the cone and a stationary flat plate. The resistance to the rotation of the cone produces a torque that is proportional to the shear stress in the fluid. The amount of torque is displayed digitally. A commercially available viscometer is illustrated in Figure 7-3fi. 

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