Viscometers measure viscosity, the resistance of fluids to flow or stress. In common terms, viscosity is related to a fluid’s “thickness”—a physical property of great interest to manufacturers of liquids, slurries, and pastes. Viscosity is a critical characteristic of foods (e.g., dairy, honey, syrup, soft drinks), paints, cleaners, adhesives, polymers, fuel oils, and pharmaceuticals. Many industries use viscosity as an endpoint in the manufacture of liquid-formulated products.
Top 6 Questions You Should Ask When Buying a Viscometer
1. What kind of temperature control and spindle rotational speed control does the instrument offer? Temperature is critical, since viscosity generally rises as a fluid cools. Spindle rotation may also affect viscosity.
2. What range of accessories (ex. sample holders) does the company offer for the instrument?
3. How easy to use is the viscometer? Since most users nowadays aren’t experts, an easy-to-use instrument is probably the best fit for most labs.
4. What are the sizes of the samples you’ll be working with? This may be an issue when analyzing very expensive materials such as drugs or proteins and cost of ownership is also important for high-volume applications.
5. What is the instrument’s measurement range? If you’re analyzing petroleum, from crude oil to gasoline, do you want to change out the capillary for each measurement, or use something that works all the way through?
6. What kind of service and support does the company provide?
Fast Facts on Viscometers
• Viscometers range in cost from about $100 for simple mechanical viscometers to $15,000 automated instruments. Rheometers, which measure viscosity and related properties, may cost as much as $200,000.
• Viscometry is an old technique, as illustrated by the persistence of mechanical viscometers. But while manufacturers continue to fine-tune more-sophisticated electromechanical rotational viscometers, the underlying technology hasn’t changed much.
• Twenty years ago, most viscometers users had an academic specialization in viscometry or rheology. Today the specialists are gone and users tend to be generalists.
• Viscosity measurements are usually conducted on dilute solutions and at varying concentrations. Measurement of the viscosity of polymer solutions at different strengths, for example, provides estimates of secondary properties such as intrinsic viscosity, molecular weight, and chain length.
• Rheometers are closely related to viscometers in that they measure viscosity and yield stress. Where viscometers determine a fluid’s “thickness” under native conditions, rheometers measure it as a function of applied shear or stress.