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Rotational rheometer
Supervisor: Davide Gardini
Rotational rheometer is an instrument that allows the measurement of the rheological properties of liquid systems (pure liquids or their mixtures) and structured fluids such as, e.g., suspensions, emulsions and polymeric solutions.
Main characterizations
- Flow curve (viscosity dependence on shear rate).
- Thixotropy (dependence of viscosity on time) by applying shear rate or shear stress step tests.
- Yield stress (shear stress below which the motion is not appreciable) by using shear stress ramp tests or the application of constant shear stresses with increasing intensity.
- Viscoelasticity (elastic and viscous components of structured fluids) by dynamic tests (small amplitude oscillatory shear flows) or static tests (application of constant stresses or strains).
- Electrorheological behavior (rheological properties dependence on external electric field applied.
Principle of operation
The sample between the two measuring elements (rotor and stator) is put in motion by dragging due to the rotation of the rotor. From the measurement of the torque and angular speed of the rotor, once known the geometric parameters of the geometry used, the shear stress and shear rate are obtained; their ratio provides the viscosity. The determination of the viscoelastic properties – elastic (or storage) modulus G’ and viscous (or loss) modulus G” – is made by applying small oscillations and measuring torques and displacements.
CNR-ISTEC owns of two controlled stress rotational rheometers:
Bohlin Instruments C-VOR 120
- Torque range: 10-4– 120 mN/m.
- Angular speed: 10-5– 650 rad/s (150 rad/s max for coaxial cyilnders).
- Oscillation frequency: 10-6-150 Hz.
- Available geometries: coaxial cylinders (C14, C25, DG40/50); plate-plate (PP20, PP60), serrated plate-plate (SP25, SP40), cone-plate (CP1/40, CP4/40); vane tool with 4 blades (V14-4B).
- Available accessories: Solvent trap.
- Thermal control unit: software-controlled water jacket (Julabo KTB30).
Haake MARS III
- Torque range: 10-6– 200 mN/m.
- Angular speed: 1.05 10-8– 157 rad/s.
- Oscillation frequency: 10-6-100 Hz.
- Available geometries: coaxial cylinders (CC25, Z21ER, Z22ER); plate-plate (P15ER); cone-plate (CP4/40).
- Available accessories: Electrorheological device, solvent trap.
- Thermal control units: Peltier Plate 60 mm, Peltier Cylinder 25 mm, water-jacket thermocryostat for cylinders Z21ER and Z22ER.
