Rheometry refers to the experimental technique used to determine the rheological properties of materials; rheology being defined as the study of the flow and deformation of matter which describes the interrelation between force, deformation and time. The term rheology originates from the Greek words ‘rheo’ translating as ‘flow’ and ‘logia’ meaning ‘the study of’, although as from the definition above, rheology is as much about the deformation of solid-like materials as it is about the flow of liquid-like materials and in particular deals with the behavior of complex viscoelastic materials that show properties of both solids and liquids in response to force, deformation and time.
There are a number of different rheometric tests that can be performed to determine flow properties and viscoelastic properties of a material which depend largely on the type of rheometer being used and its capabilities. These include yield stress.
How does it work?
A sample is forced to extrude through a barrel or die of well-defined dimensions under high pressure. The pressure drop across the barrel or die is measured to give pressure-flow rate data for the fluid, from which viscosity is calculated. Temperature and shear rate can be closely controlled to simulate the processing environment of interest.
What is it useful for?
Originating in the polymer industry, capillary rheometry is useful for measuring the viscosity profiles of suspensions and slurries containing relatively large particles, at high particle loadings. Industrial examples include polymer melts, ceramic slurries, foodstuffs, inks and coatings. Capillary rheometers, such as our Rosand range, can apply very high force, which enables the exploration of behavior at far higher shear rates than is possible with rotational rheometry. High shear rate performance is pertinent in many industrial processes, such as extrusion and spraying. For certain applications the sample size required for capillary rheometry, around a liter for the generation of a flow curve, is a limitation.