Rheometry

A rheometer is a device used to measure the rheological properties of many commonly-used materials. The measurement of rheological properties is applicable to all materials from fluids such as dilute solutions of polymers and surfactants through to concentrated protein formulations, to semi-solids such as pastes and creams, to molten or solid polymers as well as asphalt. Rheological properties impact at all stages of material use across multiple industries – from formulation development and stability to processing and product performance. The type of rheometer required for measuring these properties is often dependent on the relevant shear rates and timescales as well as sample size and viscosity.

How it works. A sample is loaded between two plates, or other similar geometry (cone and plate). A rheometer is capable of subjecting the sample to either a dynamic (sinusoidal) or steady shear strain deformation, and then measuring the resultant torque expended by the sample in response to this shear strain. Shear strain is applied by the motor; torque is measured by the transducer. Strain amplitude and frequency are set by the operator, with the actual sample deformation determined by the measured motor and transducer displacement. A rheometer is capable of measuring viscosity and elasticity of non-Newtonian materials under a wide range of conditions. Some of the most important properties that can be measured using a rheometer include viscoelasticity, yield stress, thixotropy, extensional viscosity, creep compliance and stress relaxation behavior.