Difference between Viscometer and Rheometer

Inorder to know the difference between viscometer and rheometer, we should first of all know the difference between viscosity and rheology. Viscosity is a measure of the resistance of fluid or liquid to an applied stress or shear force. In common terminology, it means the thickness of a fluid or gas. For example, water has a low viscosity so it looks thin while honey has a higher viscosity so it looks thick. Rheology on the other hand is a complex study of the flow of matter. Basically, it studies liquids and also other forms of liquids like soft solids, gels, pastes, sludges, muds, suspensions, polymers, and even sold materials that exhibit some level of flow, including petrochemicals and biological materials.

Viscosity and rheology are measured by testing methods based on rotational devices that rotate a spindle merged in a sample. By applying a controlled force and measuring the resulting force, it is possible to measure viscosity and rheological properties of a material. The two most common instruments used are viscometer and rheometer.



The difference between a viscometer and rheometer is basically the components quality and control capabilities. A rotational viscometer is a device in which a spindle rotates in a single direction. Viscometers are limited to be applied to more viscous materials. It is suitable for simple material, production or process tests that need simple flow measurements. It is more or less portable an d hence can be used to do remote or field testing, and highly suitable for quality control testing.

On the other hand, a rotational rheometer provide greater characterization of flow and deformation behavior. Oscillatory motion is applied to the spindles using rheometers. They can also apply large step changes in stress and strain to fine both viscoelastic and flow properties. Rheometers usually use ultra-low friction air bearings which are more sensitive to low viscosity samples to be measured. Rheometers can also perform other tests under a wider range of conditions. The increased versatility of a rheometer makes it a perfect tool for research, product and process development and quality control testing.



Both the instruments are complimentary. In a laboratory, both the instruments are in use, depending on the product that is to be tested.