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Rheology has been properly
defined as the study of the flow and deformation of materials. The relationship between stress and
deformation is a property of the material. We can therefore define Rheology as the study of
stress-deformation relationships.
Rheometer is
a mechanical spectrometer that is capable of subjecting a sample to either a dynamic (sinusoidal)
or steady (linear) shear strain (deformation). Then measuring the resultant torque expended
by the sample in response to the shear strain (shear strain is applied by the motor- torque
is measured by the transducer). In the dynamic mode, the motor begins all tests at the motor
zero position, and drives symmetrically about motor zero to the strain commanded by the
software. The motor is labeled with graduations indicating 0.1, 0.25, and 0.5 radians from
motor zero. The maximum angular deflection of the motor is 0.5 radians from either side
of motor zero. In the steady mode, the motor can begin a test from any position,
rotating either clockwise or counterclockwise as specified by the user using software.
Different geometry can be used for measurements. Please see an overview:
Â
| Geometry | Application | Advantage | Disadvantage |
|---|
| Cone/plate | Fluids, melts Viscosity > 10 mPas | True viscosity | Temperature ramp difficult |
| Parallel Plate | Fluids, melts Viscosity > 10 mPas | Easy handling, temperature ramp | Shear gradient across sample |
| Couette | Low Viscosity samples <10 mPas | High shear rate | Large sample volume |
| Double Wall Couette | Very low viscosity < 1 mPas | High shear rate | Cleaning difficult |
| Torsion Rectangular | Solid polymers, composities | Glass to rubbery state | Limited by sample stiffness |
- When a variety of cones and plates are available:
- 1. Low viscosity (milk)- 60 mm geometry.
- 2. Medium viscosity (honey)- 40 mm geometry.
- 3. High viscosity (caramel)- 20 mm geometry.
Please contact Krystyna
Brzezinska (kbrzez@mrl.ucsb.edu)
to schedule training. Before training starts please read MANUAL.
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