Experiment 55 Rotational Viscometry

Prepare 500 mL of a 2% solution of carboxymethylcellulose, sodium salt, in water in the manner described in the U.S. Pharmacopeia reference above. Since the solution preparation is time-consuming, your instructor may prepare it ahead of time. Using a rotational viscometer with an appropriate spindle and a constant temperature bath, measure the viscosity of this solution at various temperatures. Plot viscosity vs. temperature. 

Part B Determination of the Concentration of Carboxymethylcellulose, Sodium Salt, in an Unknown 

Prepare a carboxymethylcellulose solution as in Part A. Prepare dilutions to bracket the suspected concentration in the unknown. Measure the viscosities of the solutions and the sample with a rotational viscometer and in a constant temperature bath set at 25°C. Plot viscosity vs. concentration and determine the concentration in the unknown. 

Maintain the logbook for the equipment used in this experiment (Parts A and B), recording your name(s), the date, and the experiment number and name. 

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In a research and development laboratory at the Dow Chemical Company in Midland, Michigan, rotational viscometry experiments on various dilutions of a test fluid, such as corn syrup, can generate the required data. Once various challenges are overcome, such as obtaining a uniform and constant temperature throughout the fluid and dealing with unusual physical behaviors of the test fluid, accurate viscosity measurements can be made and the project to optimize mixing performance can move forward. 

A rotating body immersed in a liquid experiences a viscous drag or retarding force, and this principle can be applied to viscometry. The chief advantage of rotational viscometry is that continuous measurements at a given shear stress or rate of shear can be made over extended periods of time. Thus time-dependent changes in flow properties can be measured conveniently. Another advantage of rotational viscometry is the ease with which shear rate can be altered. 

To determine rheological parameters such as the yield stress and effective viscosity of a foam, commercial rheometers are available rotational and conlinuous-lfow-tubc viscometry are most commonly employed (See also Rheology). However, obtaining reproducible results independent of the sample geometry is a diflicull goal which arguably has not been achieved in most of the experiments reported in the scientific lileralure... 

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