Rotational rheometry is a powerful technique for the measurement of complex shear rheology across all material types – sensitive enough to measure the viscosity of dilute polymer solutions, and yet robust enough to measure the viscoelasticity of high modulus polymers or composites. Rotational rheometry is ideal for discerning structural and compositional changes of materials, which can be critical controlling factors in flow and deformation properties, and ultimately product stability and performance.
The basics of the rotational rheometry technique are as follows:
- The sample is loaded into the gap of a measuring system, or geometry – such as a cone and plate or a concentric cylinder system – specifically designed to impose simple shear flow when rotated.
- The measuring system is supported by a virtually frictionless air-bearing, and driven by an ultra-low inertia motor, coupled to an ultra-high precision position encoder. The sample and measuring system are also temperature controlled.
- Various rheological characteristics of the sample can be determined by rotating, oscillating or applying a step function to the measuring system – either by controlling motor torque (stress controlled rheometry) or position change (strain controlled rheometry).
- Common test modes are rotational (or flow) to measure shear viscosity, and oscillation to measure dynamic material properties such as viscoelastic modulus and phase angle.
Rotational rheometry also enables other rheological properties to be evaluated, including yield stress, thixotropy, creep and recovery and stress relaxation.